In this new series of articles, we’ll be taking a look at players around the Scottish Premiership and beyond that are knocking on the door of a move to a bigger club. It’s no secret that Celtic and Rangers like to hoover up the best talents that Scotland has to offer, so we’ve decided to look at some exciting prospects that could one day make the jump to the Old Firm.

With Celtic’s £5million summer signing Vasilis Barkas struggling to fully convince since touching down in Glasgow and his counterpart at Ibrox, Allan McGregor, considering hanging up his gloves at the end of the current campaign, this summer could be a big one for both halves of the Old Firm.

It’s not beyond the realms of possibility that the two Glasgow giants will go into the 2021-22 season with a new No. 1 between the sticks and while it can be tempting to look abroad in search of a new shot-stopper, Celtic in particular may be after someone a little closer to home this time after Barkas’ difficulties in settling in.

Luckily for both clubs, there’s already a goalkeeper in the Premiership that looks like he could fit the bill for one of Glasgow’s big two. It might only be his debut season in Scotland’s top flight but he has already shown that he is destined for bigger and better things.

Dundee United fans won’t thank me for shining a spotlight on Benjamin Siegrist but the 28-year-old Swiss hasn’t just been one of the Terrors’ best players this season – there’s an argument to be made that he’s been the best goalkeeper in the entire league.

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Allow me to run some numbers past you. First off, we should point out that Siegrist is playing for a newly-promoted side experiencing their first top-flight campaign in years. As such, perhaps it’s no surprise to learn that Siegrist is the fourth busiest keeper in the league this term, facing on average 4.7 shots per 90 minutes played. Additionally, the former Aston Villa youth player has nine clean sheets to his name this season – only McGregor, Aberdeen’s Joe Lewis and Hibs’ Ofir Marciano have more.

Siegrist is facing a lot of shots, relatively speaking, but he is doing an admirable job of keeping them at bay; around 77 percent of shots on his goal are repelled by the one-time Switzerland Under-21 internationalist, a figure only bettered by Rangers pair McGregor (87 percent) and Jon McLaughlin (84.6 percent).

All this sounds fairly impressive until you look at the number of goals Siegrist has conceded this season. As many as 31 shots have found their way into the back of the net in Siegrist’s 27 Premiership appearances to date, meaning he concedes 1.09 goals per 90 minutes. There are eight goalkeepers with at least 700 minutes under their belts that concede goals at a lesser rate.

So why are we excited about Siegrist then? The answer can be found when we get into some under-the-hood stats, like Expected Goals Conceded (xGC).

This stat works fairly simply – the odds of each chance a keeper faces is given a probability of a goal being scored, which is then converted into a decimal value between 0 and 1. This gives us the Expected Goals (xG) of the chance (so a shot that had a 50/50 chance of going in would have an xG of 0.5, for example). At the end of the game, we add up the xG of all the chances a goalkeeper faced and this gives us the xGC. It’s a way of showing that some saves are better than others, and it tells us if a particular goalkeeper is over or under performing. If a keeper’s xGC is higher than their goals conceded, then we can deduce that they are preventing goals that should really be going in.

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Siegirst has the fifth-highest xGC per 90 minutes played of any keeper in the league with a significant number of minutes under their belts this season, and should concede 1.36 goals per game. Eagle-eyed readers will notice a discrepancy between Siegrist’s goals conceded and xGC per 90 and in statistical circles, it’s a fairly sizeable one: there are around 0.27 goals per game that he should really be conceding, but isn’t. Why? Because he happens to be a very good goalkeeper.

When we subtract a keeper’s goals conceded per 90 from their xGC per game, we’re left with a stat called Prevented Goals. This is exactly what it sounds like – a calculation to determine how many goals a keeper has prevented for his side above what can be reasonably expected.

Siegrist has a higher prevented goals per 90 minutes played than any other goalkeeper in the league, bar none. He is one of just eight goalkeepers in the league that can legitimately claim to be overperforming this season and per game played, he’s preventing more goals that should really be going in than anyone else.

With his contract due to expire at the end of next season, United may well decide to cash in on their prize asset this summer rather than risk losing him for nothing a year later. It’s inevitable there will be interest in the Swiss shot-stopper’s services from afar and I suspect there are a few clubs already casting admiring glances his way. But if push comes to shove and Celtic or Rangers find themselves in the market for a new goalie, they need only look as far as Tannadice.