Steven Naismith has had a scan on his injured knee, with Rangers expected to announce the result on Tuesday morning.
The in-form forward was stretchered off in Saturday's 2-1 win at Aberdeen following a clumsy challenge on midfielder Rob Milson.
And the fear is that the 25-year-old has suffered damage to the anterior cruciate ligament in his right knee.
Naismith suffered a ligament problem in his left knee in 2008 that ruled him out for eight months.
Rangers say the Scotland international was seen by a consultant today, with scans taken of the damaged area.
And the Ibrox club hope to receive a full prognosis later on Monday before releasing details.
Naismith is the Scottish Premier League's leading scorer with nine goals and manager Ally McCoist was downbeat following the win at Pittodrie.
"The signs aren't good, but we won't know until we get a scan and a full diagnosis," he said on Saturday.
"I would have to say it probably isn't looking good at the moment as he says he feels the same pain and numbness as he did when he did it the first time.
"It's strange because I thought our team played some great stuff in the second half and thoroughly deserved their victory, but there is no doubt the shine has been taken off the result by Steven's injury."