The Brazilian picked up the injury against QPR on Saturday and boss Andre Villas Boas is fearful.
He said: “It’s not so bad in terms of knee injuries. He’ll have the MRI on Sunday and we’ll know the full extent. Hopefully he is going to avoid an operation and he is going be back soon.
“We have to know the extent of the injury – eventually with treatment we could look at a four-week period, maybe more, hopefully not.”
