Five other high-profile transfers to Celtic and Rangers which ended up falling through

But Turnbull, who is going to have to undergo a knee operation after a problem was detected in his medical and is set to be sidelined for the first half of the 2019/20 season, isn't the first player to have his hopes of joining one of Glasgow's big two clubs dashed.

Here we look at five other moves to Ibrox and Parkhead which fell through and the reasons behind them failing to come off.

MO JOHNSTON TO CELTIC IN 1989

The most infamous episode in Scottish football transfer history took place in 1989 after Rangers had reclaimed the Scottish league title from their city rivals.

Maurice Johnston, the former Celtic striker who had moved on to French club Nantes two years earlier, had made it known to Roy Aitken on Scotland duty that he would be open to a return to his old club.

A record £1.25 million transfer fee was struck between the two clubs and Johnston signed a letter of intent – akin to a modern pre-contract agreement - stating he would become a Celtic player on July 1.

Celtic chairman Jack McGinn and director Chris White flew to France to pay Nantes a £400,000 deposit.

Despite the fact the player hadn’t actually signed a contract, Celtic decided to unveil their new signing to the media eight days before the Scottish Cup final against Rangers.

Legend has it that McGinn told Johnston to “pretend” he had signed. “I don’t want to play anywhere else,” the player said.

But after Celtic had beaten Rangers 1-0 in the final the deal fell through and he ended up joining the Ibrox club.

Johnston’s agent Bill McMurdo, a staunch Rangers fan, is blamed by many Celtic fans for the unexpected turn of events.

But years later Billy McNeill, the then Parkhead manager, claimed the Celtic board were at fault because Nantes didn't receive the balance of the fee.

“The only reason Celtic didn't get him was because they still had £700,000 to pay Nantes, and if they had paid that, he would have been our player,” said McNeill.

Johnston became, to the disgust and outrage of many Rangers fans as well as Celtic supporters, the first high-profile Catholic player to sign for the Govan club on July 10, 1989.

JARDEL TO RANGERS IN 1996

Brazilian striker Mário Jardel de Almeida Ribeiro was paraded on the pitch at Ibrox in Rangers training kit before a match against Raith Rovers in 1996 and then took in the game from the stands.

But work permit regulations and strict rules about the number of non-EU players who could represent a club scuppered the multi-million pound transfer from Vasco da Gama.

At the time it was suggested that the Scottish Football League could only sanction 10 work permits and had given the last one to Kilmarnock for their Ghanian defender Sammy Adei.

Hamish Walker of the SFL said: “We have received this application for Adei from Kilmarnock and we will now advise the Home Office of the details. It will be up to them to decide if it will be granted or not but, by the terms of the Scottish League management committee decision, Rangers will not now be able to apply on behalf of their player until this situation regarding Adei is decided.”

Jardel went on to score 166 goals in 169 appearances for Porto in a four year period and win 10 caps for his country.

Rangers tried in vain to sign the 6ft 2in forward again in 1997, 2001 and 2003. But their efforts were to no avail. It was the transfer which was fated never to happen.

JOHN HARTSON TO RANGERS IN 2000

John Hartson became a hero to Celtic fans during his five years at Parkhead. The big Welsh striker scored 109 goals in all competitions, won the Scottish title three times, the Scottish Cup twice and the League Cup once. His strikes against Liverpool and Celta Vigo were also instrumental in his side reaching the UEFA Cup final in 2003.

But the big Welshman very nearly ended up signing for the other half of the Old Firm. He had been on the verge of putting pen to paper with Rangers just a year earlier only to fail a medical. He was flown from Cardiff to Glasgow on then owner Sir David Murray’s private jet, taken to Ibrox to be shown around and then whisked off to Ross Hall Hospital.

But just as the Wimbledon forward was set to agree a five year deal he was told a scan had shown a problem with his knee. The deal fell through and he joined Celtic in a then record £6 million transfer the following year. The rest is history.

SCOTT MCDONALD TO RANGERS IN 2007

Scott McDonald may have broken Celtic supporters’ hearts when his late double for Motherwell against the Parkhead club at Fir Park on Helicopter Sunday in 2005 denied them the Scottish title.

Yet, the Australian striker is still remembered fondly by supporters of the East End club for the goals that he scored in his three seasons there, not least those against Spartak Moscow, AC Milan, Manchester United, Rangers and Dynamo Moscow.

“Skippy”, though, was another player who very nearly put pen to paper with the Ibrox club. Rangers had a £400,000 offer turned down by their Fir Park rivals in the final days of the January transfer window in 2007.

Motherwell manager Maurice Malpas was reluctant to part with his leading goalscorer halfway through the season. “I completely understand Maurice's decision," said Rangers manager Walter Smith. "We would have liked to get Scott on board, but Motherwell have to do what they believe is right for them.”

The player was devastated. “When my agent called to tell me what was happening, I was on top of the world,” he said. “It's so hard for me to take. But it's up to Motherwell to call the shots. Hopefully, I can get over this.”

Malpas was vindicated in his decision – the 23-year-old scored 15 league goals that term to help the Lanarkshire club remain in the top flight.

His form attracted the interest of Gordon Strachan. Celtic tabled an identical £400,000 offer for McDonald in March that was accepted. He banged in 31 goals for his new club the following season and helped them pip Rangers to their third consecutive Scottish title.

JOHN MCGINN TO CELTIC IN 2018

Having been tipped to take over from Scott Brown in the Scotland midfield, and possibly even as captain of the national team, for many years it was no great surprise when it emerged that Celtic were interested in signing John McGinn from Hibernian last summer.

McGinn had been a lifelong Celtic supporter and season ticket holder - his grandfather Jack is the former Celtic chairman - and was keen on the move. But the Parkhead club made three separate offers during July last year only for them all to be rejected.

“It was hard for me,” said the player. “I had my heart set on it. But two months along the line it became quite clear that a deal wasn’t getting agreed. It was quite hard for me.”

Aston Villa entered the fray and he signed for them in a £2.7 million transfer last August. McGinn helped the Birmingham club win promotion to the Premier League via the play-off final, which he scored the winning goal in, last month.