Celtic have confirmed midfielder Joe Ledley will miss the rest of the season because of a hamstring problem.
The Welshman hobbled off in the 55th minute of the goalless Old Firm match on Sunday, replaced by Kris Commons.
He had been absent from the club's match at Kilmarnock last Wednesday but the gamble to play him in the crunch game at Ibrox backfired.
Ledley will miss the last five games in the Scottish Premier League title race, plus the Scottish Cup final.
The 24-year-old has played 29 times for Celtic this season but some comfort for manager Neil Lennon is the depth of his squad, with James Forrest replacing Ledley against Kilmarnock and Commons coming on for him at Ibrox, while Shaun Maloney has returned from injury.
The former Cardiff City player injured his hamstring in the recent Scottish Cup semi-final win against Aberdeen and will now be a spectator in the cup final against Motherwell at Hampden.
Meanwhile, former Celtic striker John Hartson feels the club's fans have yet to see the best of Ledley.
He told BBC Radio Scotland's Sportsound on Monday: "He's got all the attributes: he's a great athlete, he's got a good left foot, he's very combative in the tackle, he likes to put his foot in, he will get forward for you and give you that goal threat and defensively he will work back.
"He's still only in his mid-20s so hopefully he'll have a long Celtic career ahead of him. He hasn't pulled up trees but he's had a decent season considering it's his first one.
"It's never easy settling in to a new club."