Rangers' Alfredo Morelos is a doubt for Sunday's Old Firm clash after being spotted on crutches days ahead of the match at Ibrox.
The striker is recovering from a thigh injury and was at Glasgow Airport on Thursday, departing for a reported scan in London.
Morelos picked up the knock while on international duty with Colombia and was unable to take part in his country's 3-0 World Cup qualifying win against Bolivia.
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The 25-year-old, who has scored 12 goals in 26 league appearances this season, returned early from international duty for treatment but now faces a battle to recover for Sunday's match at Ibrox, live on Sky Sports Football.
A statement from the Colombia Football Association read: "The coaching and medical staff of the Colombia Men's Senior National Team reports that, after performing medical examinations on player Alfredo Morelos, a muscle injury to his left thigh was confirmed, which prevented him from participating in the previous commitment against Bolivia and in the same way does not allow him to participate in the next match of the Qualifiers for the FIFA Qatar 2022 World Cup.
"For this reason, the striker is called off to begin his recovery work. We wish the player a good return to his club."
Thomson: Rangers need quick start
Former Rangers midfielder Kevin Thomson believes the Ibrox side have to start Sunday's game on the front foot if they are to inflict revenge on Celtic for the last Old Firm meeting in February.
Celtic were 3-0 up by half-time that night and Thomson believes Giovanni van Bronckhorst's side can do the same this weekend as they look to reduce their rivals three-point lead in the Scottish Premiership.
He said: "Rangers have to be on the front foot.
"Celtic showed energy at Celtic Park in the last game and they blew Rangers away.
"Rangers have the capability to do the same thing and the crowd could be massive on Sunday.
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"The energy they produce at Ibrox is unbelievable and the players will need that.
"They also need to give the fans something to get excited about and that will be the key, the way they start.
"If they start sharp, create early tackles and chances as well as impose themselves on the game, that could be a defining factor in the game.
"There is pressure on both teams ahead of Old Firm games. Celtic have the bragging rights, being top of the league, it's a massive game for Rangers.
"It's so tight and they are good teams but if Rangers can bring their European form they have the chance to win.
"Celtic will know if they go to Ibrox and win, then it could be curtains for Rangers."
McCoist: Old Firm defeat 'unthinkable' for Rangers
Ally McCoist believes defeat for Rangers in Sunday's Old Firm clash would end their defence of the title - but he cannot see his former side losing to Celtic.
"It's one of the biggest Old Firm games, certainly the biggest for a while," McCoist told Sky Sports News. "I don't think Rangers can afford to get beat.
"Postecoglou has done a great job at Celtic and they have put themselves in a very good position. There's three games coming up in the next month or so, if you include the Scottish Cup semi-final [between the Old Firm clubs], so there won't be a dull moment north of the border, particularly in the Glasgow area.
"But from Rangers' point of view, defeat is unthinkable as I think it would make the gap [to Celtic] far too big.
"But I don't see that, I think both teams have a little bit of form. Rangers in Europe have been excellent, domestically the form's been a little bit up and down. They had a massive win at Dundee where they didn't play particularly well, but they are hanging onto Celtic's coattails. And with this game coming up, I think we're going to see a different Rangers.
"It's a game they certainly cannot afford to lose and I think they'll certainly go about their business in a manner that they have to win the game."
McCoist also highlighted Rangers midfielder Aaron Ramsey as a key factor while considering Rangers' chances of coming out on top at Ibrox.
"He's class isn't he? He's a wonderful football player," McCoist said when asked about Ramsey. "It's been highly documented that he's struggled a little bit with injuries to keep him 100 per cent fit, which is a great shame because we all want to see good players on the pitch and he's certainly that.
"He'll have a real bonus after scoring his first goal up in Dundee and I think he played the entire game [for Wales]. That's a real positive in terms of his fitness and I'm very hopeful that he can get his feet up, have a rest and get himself ready for this Old Firm game because I want to see Aaron Ramsey playing in that."