Rangers manager Ally McCoist hopes Kyle Bartley will only be out of action for a further month after the on-loan Arsenal defender underwent surgery.
The 20-year-old had a hernia operation on Tuesday after coming off during last month's 2-0 win over Inverness Caledonian Thistle.
"It's a big disappointment for Kyle himself that he's out for a bit longer.
"But I had a good chat with him last night after his operation and he's upbeat," McCoist told Rangers' website.
Bartley, who is in his second loan spell at Ibrox and also suffered a knee injury last season, had returned to Arsenal two weeks ago, with the Barclays Premier League club deciding to send him for surgery.
"With the attitude he has and what he gives us, being without him is a big miss for ourselves, but we won't rush him back," said McCoist.
"I'd hope we'd have him back in around four weeks or so, but we'll take as long as he needs to make sure he is fit again."
However, Rangers' options in central defence will be enhanced for this weekend's meeting with Dundee United in the Scottish Premier League.
Dorin Goian and Sasa Papac, who had been sidelined in recent weeks, played 90 minutes for Romania and Bosnia respectively this week, as did versatile defender Steven Whittaker for Scotland.
Late decisions will be taken on the fitness of striker Kyle Lafferty and midfielder Lee McCulloch, but veteran centre-half David Weir will again miss out and left-back Lee Wallace has targeted the Old Firm derby on 18 September for his own return.
Wallace, who signed from Hearts during the summer missed matches against Maribor and Aberdeen with a hamstring injury, said: "I'm working hard with the physios and I'm aiming to be back as soon as possible, but I've just had to be a bit careful after being out for a long while last season.
"The Celtic game is a huge one for the club and that's certainly one I'd look to be involved in if I can be.
"When you come to a club like this, that's the type of match you want to take part in.
"It's massive for both sides and when you win it's just great.
"I want to be a part of it all and, although it has been tough for the manager with the bad luck we've had lately with injuries, I hope to be back for that one."