The central defender has still to gain the work permit to play for Celtic, but this should be resolved early this week, according to manager Neil Lennon.
No precise estimation can be put on Ambrose's potential to cure the ailment at the heart of Celtic's woes but he faces great expectations. The search for a centre-half at Parkhead has taken on mythical proportions. Ambrose is the latest to audition for the role that has caused heartbreak to Celtic's fans and no little joy to opposing teams.
The recipe for defeat by St Johnstone included a variety of ingredients. Celtic did not play well after taking an early lead, with a lack of urgency and creativity being apparent. Good players gave bad performances. In particular, James Forrest was ineffective and Gary Hooper was almost harmless, with the rest mediocre at best.
Lennon did not spare his side after the match, describing Mikael Lustig, Kris Commons and Kelvin Wilson "as the exceptions" to his withering criticisms. He will have his reasons for these choices but only Fraser Forster in goal and Commons left Perth without a significant blemish on their reputations. The Scottish internationalist scored Celtic's goal with a drive after four minutes but this lead was never protected.
Wilson and Lustig both played their parts in the goals that Celtic lost to ensure the heavy favourites for the championship have won only two matches in the Clydesdale Bank Premier League this season. The first came when the champions' central defence of Wilson and Charlie Mulgrew offered Gregory Tade too much space and Rowan Vine's simple, effective pass was driven home by the Frenchman. Lustig, too, was easily dismissed as Vine cut in to score the winner.
This defensive frailty has been like some recurring, debilitating virus for Celtic.
Tade, the man of the match who set the bar for an energetic, committed performance from St Johnstone, has his strengths but he should not be able to cause the mayhem he did on Saturday.
Celtic supporters, though, may remember the havoc Tade inflicted at Celtic Park on another couple of defenders who ultimately failed auditions. An afternoon against Inverness Caledonian Thistle was both bruising and revealing for Glenn Loovens and Daniel Majstorovic. Tade has moved on to St Johnstone but Celtic have not yet found certainty in central defence.
Thomas Rogne replaced the disappointing Emilio Izaguirre and was more effective in combating Tade. At 22, the Norwegian has promise and has come far since his buffeting by Nikica Jelavic in the 2011 Co-operative Insurance Cup final, but Ambrose now has an excellent chance to partner him in central defence.
Wilson has never fully convinced, though he shows good pace, and Mulgrew always resembles a player filling in at centre-half. The Scotland cap, with his composure and height, would be an ideal candidate as one of a back three, an option that Lennon considers with some seriousness of purpose.
However, on Saturday the old failings in defence yet again cost Celtic. St Johnstone, disciplined and motivated, defended doggedly and with some fortune, not least when profiting from Euan Norris's decision not to award a penalty after Steven Anderson brought down Commons. But it would be a misrepresentation to say that St Johnstone "nicked" this victory.
Tade, Vine and Peter Pawlett created chances, while Celtic were restricted to glimpses on goal. Tony Watt, the substitute, had the best chance to equalise, with almost the final kick of the ball, but Alan Mannus saved with his legs.
Lennon was right to accuse his side of a lack of drive and creative force. However, he will know that a solid defence ensures that one-goal leads can be defended no matter what is happening or not happening in the front six. Midfielders and forwards, of course, have a defensive role to play in modern football but the goals that were lost came from lapses by the back four.
"I don't think we were great against Celtic, we were hard to play against and tried to play off the back of that – that's what we're good at," said Dave Mackay, the St Johnstone defender, with honesty and no little accuracy. Of Tade, he added: "Gregory does a great job for the team. He's not pretty on the eye at times but he's a handful and the Celtic centre-halves knew they were in a real game."
Another "real game" awaits as Oscar Cardozo prepares to inflict the same sort of match-winning damage as he did against Celtic five years ago. Aficionados with longer memories will also remember the night in 2006 in Lisbon when Gary Caldwell, another auditioner for the Celtic centre-half role, muffed his lines, scoring an own goal.
His defenders will state that he now plays in the Barclays Premier League. His detractors will remember him as the only centre-half ever to be hit on the back of the head by a long kick-out from the opposing goalkeeper in a Champions League match.
The search for a stopper continues. Ambrose, with 14 caps for Nigeria, is next up. First, he needs a permit – then he will face the tests.
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