The French international, who has impressed since joining the Eagles on loan from Liverpool in January, was forced off through injury in the second half of Wednesday night’s 1-0 loss to Tottenham at Selhurst Park.
Sakho’s studs appeared to get caught in the turf as he attempted to dispossess Harry Kane, twisting the defender’s knee in the process. He left the field on a stretcher while wearing a knee brace.
“It’s a ligament injury, which ligament we don't know,” said Allardyce, who is already without centre-backs Scott Dann and James Tomkins through injury.
“We hope it's not the cruciate. It could be medial or lateral, but certainly a hyperextension of the knee. We will see after a scan.
“We won't know if any of our three injured centre-halves will get fit again.”
Sakho has played a major role in Crystal Palace’s recent resurgence, helping to tighten up the side’s backline.
Palace paid a £2m loan fee to bring the Frenchman to Selhurst Park and agreed to cover his £100,000-a-week wages.
It’s unclear if the club will move to sign Sakho on a permanent basis given Liverpool’s expected asking price which is understood to be above and beyond £20m.
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies