Tottenham midfielder Sandro looks likely to miss the first two months of the new Premier League season after undergoing knee surgery on Friday.
The 22-year-old returned to London having felt the injury training for Brazil at the Copa America on Monday.
Scans showed he had torn his lateral meniscus, and suffered a calf strain.
"The specialist has advised a three-month rehabilitation period before a return to full training," read a statement on the club's website.
Sandro had complained of pain in both his calves and his knee while on international duty in Argentina.
The Brazilian, who signed from Internacional for £8m, played 26 times for Harry Redknapp's team last season.
His injury may further strengthen Tottenham's resolve to hang on to fellow midfielder Luka Modric, who is reported to have handed in a transfer request after two bids from Chelsea were turned down.