Under-fire Vasilis Barkas ' disappointing start to life at Celtic has been blamed on weight loss.
Greece international boss John van't Schip backed the shot-stopper to come good but believes he's undergoing a steep learning curve in Scotland.
Celtic paid AEK Athens £5million for the 26-year-old to replace Fraser Forster between the sticks.
But he lost his place to Scott Bain after some ropey displays before being reinstated by boss Neil Lennon.
Fingers were pointed at Barkas after Celtic's 4-2 defeat to AC Milan on Thursday but van't Schip reckons he still has what it takes.
He said: "Vasilis has now just to concentrate on bouncing back both for Celtic and the national team.
"He lost a lot of weight since he joined Celtic too and I think he needs to adapt to the Scottish way of doing everything.
"By that I mean, the training, the games, the food, the weather, the mentality.
"Part of the job of being a goalkeeper is reacting to the pressure and criticism and I hope he will do that.
"You have to remember he was a very good goalkeeper at AEK Athens and did a really good job there.
"I still believe he is still an excellent keeper and he will show that."
