Chris Sutton has sent out a warning to Brendan Rodgers and Celtic insisting his former side must improve with rivals Rangers lurking.

The Scottish champions have stuttered in form this campaign, mainly in the Champions League, but they have also dropped points domestically.

Rangers have been far from perfect either, but Sutton fears that a League Cup victory for Philippe Clement's side could spark confidence and belief into the Ibrox squad.

He told the Daily Record: "Celtic look weak and timid in the Champions League. Worryingly for them, I'm beginning to wonder if others aren't scared of them on the home front any more and they are losing some of their own fear factor.

"Brendan Rodgers might not be able to fix the first of those. But the manager definitely needs to find a way to quickly reinstate the second because the club are walking a tightrope at the moment and can't afford to stumble.

"It's hard to pick holes in a side who haven't lost a single fixture in the league all season and have a strong lead at the summit. But, just as with Europe, there needs to be honesty. And the simple truth is Celtic are meandering in spells. Last weekend's draw with Motherwell was not a one-off in terms of performance.

"It was sluggish and it was lacklustre, just as the goalless draws with St Johnstone and Hibs were earlier in the campaign when the other points were shipped. There have also been games won where they haven't hit the heights and I'm sure opponents are gaining more belief they can get something.

"Celtic dodged a bullet last weekend because Rangers slipped up the following day against Aberdeen. However, they can't keep opening the door because, at some stage, their big rivals could walk through it. Don't get me wrong, Rangers' poor showing against Aris Limassol shows they still have away to go.

"But winning the League Cup would give Philippe Clement's side a major shot of belief and added drive to try to overhaul a deficit in the table. Just as it did for Ange Postecoglou's team in the Aussie's first season when they came back from a similar position as now to win it."

Sutton added: "Clement is saying all the right things - just as Postecoglou did - and making big calls, as we saw with Todd Cantwell on Thursday night. Celtic need to stand on the pedal, get moving and strike fear into sides again.

"Teams dreaded facing Postecoglou's 100 miles-per-hour outfit. They ran sides ragged, never gave them a breath, ravaged them. They hated it. Right now, Celtic aren't doing it. It's a different style and, just like Stuart Kettlewell seven days ago, Craig Levein will believe he can set up a St Johnstone side tomorrow to sit in, frustrate and stay compact due to a lack of thrust from the visitors.

"Celtic need a rocket. They need to get the ruthless edge back at home. If the fans are frustrated enough at the European setbacks, I would very much doubt they'll tolerate failure on the home front."