Chelsea boss Andre Villas-Boas is hopeful Ramires may have escaped serious injury against Queens Park Rangers, but fears the midfielder could be sidelined for some time.
Ramires left the field on a stretcher during Chelsea's 1-0 win at Loftus Road in the FA Cup after crumpling to the ground.
He was treated for some time on the pitch and there was real concern among the Chelsea players and staff. The Brazil international will be sent for a scan, but Villas-Boas has his fingers crossed that the problem is not serious.
"It looks like a medial ligament injury, not so bad in terms of knee injuries," Villas-Boas said. "He will have an MRI tomorrow and we will know the full extent.
"Hopefully he will avoid an operation and be back soon. We could look at four weeks, but we have to know the extent of the injury to give a good assessment."