Rangers could be forced to head into the first Old Firm derby of the season without talismanic striker Dado Prso.
The Croatian forward missed yesterday's Bank of Scotland Premier League defeat at Hibernian through injury, following a substitute appearance against Molde in the UEFA Cup on Thursday night.
He still suffers from pain in the knee which was operated on during his time at Monaco and will decide at the end of the season whether he needs to hang up his boots.
Ibrox boss Paul Le Guen knows he will need all his best players at his disposal for the trip to Celtic Park on Saturday and Prso falls into that category.
On a day when several players from both sides will make their Old Firm debuts, Prso boasts past experience of the fiery fixture.
But, asked whether he would be fit for the weekend, Le Guen said: 'I don't know yet.
'He is important for the team and he has played many important games since the beginning of the season.
'But he was injured and couldn't play against Hibs. I regret that but I had no choice.'
Le Guen also defended his decision to drop Kris Boyd in favour of Filip Sebo for the 2-1 defeat, even though he has netted five goals this season.
'It's my decision,' said the Frenchman. 'He played the whole game on Thursday and there is competition between them.
'He is not the only match-winner but he is an important player.'
Sebo - a summer signing from Austria Vienna - scored his first goal for Rangers and Le Guen remains confident he can be a success at Ibrox.
'I am convinced that he can be an important player for us,' he added. 'And, after the game, I keep this opinion.'
Last week's 4-0 SPL win over Falkirk already seems like a distant memory.
Since then, Rangers have escaped with a drab goalless draw from their UEFA Cup tie against a Molde side third bottom of the Norwegian league, before finding themselves outclassed in every department by a far superior Hibs side.
The signs do not look good ahead of the clash with Celtic, who strengthened their lead at the SPL's summit with a win over Dunfermline, following a brave 3-2 defeat to Manchester United in the Champions League.
Even so, Le Guen insists he is relishing his first Old Firm derby.
'It's a big task but it's a great task,' he said. 'It was a tough game against Hibs and we need to do better to get better results, that's clear.
'Too many players were too far from their normal level and, when that's the case, it's difficult to get a good result.
'It's frustrating but we must not give up. We must believe that we will solve the problem.'
Hibs boss Tony Mowbray believes the win over Rangers backed up his theory that his players are good enough to compete with the top teams in Scotland.
'It's important to score first against the Old Firm to stop them dictating the tempo of the game,' he said.
'We were all disappointed it was only 1-0 at half-time but we are just delighted that we have shown once again that we can compete with the Old Firm.'