'Severity' of Schmeichel injuries surprises O'Neill

Celtic, who are second in the Scottish Premiership and two points behind Heart of Midlothian, travel to face Dundee United on Sunday (12:30 GMT).

Right-back Alistair Johnston is nearing a return to fitness after being out for most of the season with hamstring problems.

"He's doing really well," O'Neill said of the Canada international.

"His national side want him to go for a week over there. We, at this minute, would probably prefer him to stay. I don't think it's going to a big issue as long as he's training somewhere.

"We need to have some sort of bounce games or something like that to play in here as soon as possible.

"That's big news if he can come back in for the part of the run-in, so that would be great."

O'Neill also said Arne Engels is "doing really fine" in his recovery and made similar sentiments about captain Callum McGregor.

Engels last played on 11 February, while fellow midfielder McGregor has missed the past two games.

"He's fine, he's going to be fine and he's come through," O'Neill said of McGregor.

"We'll see how he is tomorrow. That was his first real day with the team, but he's raring to go."