Rangers manager Ally McCoist described Kyle Lafferty's injury in the 3-0 win over Motherwell as "a big, big blow".
Doubts have arisen over Nikica Jelavic's future after he was left out of the team that beat 'Well but McCoist says the player was injured.
The 26-year-old has been linked with a move to several English clubs.
"Nikica didn't make it with a groin strain. He attempted to train yesterday and had a go this morning but he wasn't fit enough," said McCoist.
"I don't know the full extent of the [Lafferty] injury but it looks like he has pulled his hamstring and my guess would be four or five weeks."
The hamstring injury to Lafferty may halt a proposed loan move to Blackpool for John Fleck, who replaced Lafferty against the Steelmen.
"The only enquiries we have had are for John Fleck for loan, which would probably be put on the back-burner now," McCoist said.
"I'll look at the whole thing again tomorrow morning and reassess the injuries but I would have to say it would be doubtful he would be going anywhere.
"I'll sit down with [owner] Craig [Whyte] tonight or tomorrow and have a wee chat and see where we are.
"We look as though we need strengthening in forward areas. The injuries to Jelavic, Lafferty and long-term to Steven Naismith certainly hasn't done anything to change my opinion.
"As happy as we were with the performance today, we know we need bodies in. At this moment, we've got one centre-forward."
The only fit centre-forward, David Healy, opened the scoring against Motherwell and Sone Aluko and an own goal by Stephen Craigan gave Rangers a comfortable win.
Another player who has played in forward areas for McCoist's side is Thomas Bendiksen but his contract has expired and he has returned to his native Norway to hold talks with Tromso.
McCoist has been linked with a move for former Rangers striker Nacho Novo but the manager added: "Nacho was back home for Christmas and New Year and phoned us up and asked to come in and do a bit of training.
"We obviously welcomed him with open arms and the wee man looked great.
"He was the same wee Nacho that the Rangers supporters loved for many years here and he is a player that we know has been over the course and distance here.
"But, at this moment in time, I can't tell you anything other than he was looking good.
"I can't say we are interested and I can't rule out interest in any other player either."