Ahead of tomorrow's Old Firm clash, Celtic manager Martin O'Neill handed David Marshall a new four-year deal after his heroics in Barcelona on Thursday night and joked it was all downhill for the goalkeeper from now on. The 19-year-old rookie, who was standing in for the suspended Robert Douglas, was Celtic's hero in their dogged goalless draw with the Catalans in the Nou Camp which sent the Parkhead side through to the UEFA Cup quarter-finals with a 1-0 aggregate success.

Hours later the youngster committed himself to Celtic until 2008 and is set for another huge test against Rangers if Douglas fails to recover from an ongoing hip injury. But O'Neill joked: "David thinks all games are like the Barcelona one. For a young lad to step into the Nou Camp after playing so few games and played the way he did was magnificent. But as I said jokingly to him 'it's downhill after that'. We've signed him up for the next four years but it was in the pipeline anyway regardless of his performance against Barcelona."

O'Neill however, admits even he was surprised at the performance of his young goalkeeper, who kept the Spaniards at bay with a string of saves. He said: "We never had any qualms about putting him in but I don't think anybody would have made up the performance he conjured up for us. It was magnificent. I thought his first save in the first minute was a big moment in the game."

O'Neill also insists outward-bound midfielder Liam Miller still has an important role to play for the Parkhead club before he leaves for Manchester United at the end of the season. The 23-year-old Corkman upset the Celtic faithful when he signed a pre-contract for the Old Trafford club in January, and after sustaining a groin injury it was thought he had played his last game for the Hoops. But because of injuries and suspensions in O'Neill's squad, fit-again Miller made a substitute appearance in the Nou Camp.

And with Alan Thompson and Jackie McNamara carrying knocks over from Spain, Miller could find himself in O'Neill's side to play Rangers. The Celtic manager is confident if the talented midfielder does appear, then the Celtic fans will get behind him in the same way they did in Barcelona.

"As I've mentioned before, we're all disappointed Liam's going to be leaving at the end of the season, but he wants to play games," said O'Neill. "And we'll use all our players between now and the end of the season. But he's just back into the fold. He's only done a little bit of training, he had an under-21 game last Monday and then he was thrust back in again. In the atmosphere of Barcelona where everyone was fighting for the side and everyone was behind the whole team, it wouldn't really have mattered who we would have brought on at that particular stage.

"But contrary to what some people might think, I have not got a problem playing him. Whatever reaction he'll get from the Celtic fans I think Liam will be able to cope with it. But at the minute there is a tide of euphoria and if he gets a chance on Sunday and puts one in the back of the net for us, I think he will temporarily be forgiven."

Celtic travel to Ibrox with a massive 16-point lead over their rivals and O'Neill accepts victory tomorrow would allow his battle-weary players some domestic breathing space for the rest of the season. He said: "What we do know is that regardless of what happens on Sunday, we need to win four out of nine matches and we can't get beat - but that's easier said than done at this stage of the season where there is no respite."