Derek McInnes says Lawrence Shankland could be sidelined for up to three months.
The Rangers captain suffered a hamstring tear during Saturday's 1-0 victory over St Mirren.
McInnes confirmed it's a grade 2c tear, similar to the injury Shankland sustained at Hearts in January.
The club is awaiting results from a follow-up scan in London to decide if surgery is necessary.
McInnes said: "We've had confirmation he has had a grade 2c tear in his hamstring, very similar to the one he did at Hearts in January.
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"He is now getting a follow-up scan with a specialist in London to determine if he has surgery or allows it to heal naturally.
"If he has the surgery it may be three or four weeks less, but maybe that increases the risk again."
McInnes added that more will be known in the next 48 hours.
Depending on the decision regarding surgery, Shankland could be out for three to four months.
McInnes believes that avoiding surgery might speed up his return but could make him more prone to future tears.
He added: "I could see when he walked off at the weekend he knew it was significant.
"It was his very first sprint after two and a half minutes standing about [due to VAR] breaking down.
"He came back really smoothly last time and got to the World Cup."
Shankland's injury leaves Rangers with Kevin Kelsy and Ryan Naderi likely to compete for the starting spot up top.
Kevin Kelsy made his debut at the weekend following a £9million move from Portland Timbers, while Naderi scored the only goal of the match, his third of the season.
Bojan Miovski also remains at the club after a proposed loan move failed to materialise.
McInnes said: "Ryan was a significant investment; he's a handful and when he plays with a partner, he does the job and did really well at the weekend.
"The club has spent a lot on Kevin, it's a big step but we think it's the right one.
"Bojan's goals per game in Scotland is very strong.
"He's trained brilliantly and it looked as though he was maybe going elsewhere but such is the way, I'm glad we have these three lads in the building."
