The Uruguayan was injured during the second half of Napoli's 2-0 Champions League win against Spanish outfit Villarreal on Tuesday, and has lost the race to be fit in time to face Inter, according to reports from La Corriere dello Sport.
The striker scored his Napoli's vital second goal to kill off the La Liga side, but paid the price as tests on Wednesday morning showed he suffered a sprained ankle.
Reports further indicate that the 24-year-old may not be ready for selection for at least two weeks, as the full extent of his injury is still unknown.
This will upset Uruguay, as he is expected to miss their 2014 World Cup qualifiers against Bolivia and Paraguay.