The 21-year-old suffered a dead leg in training before the international break but the injury has caused his thigh to swell and he now faces an extended period on the sidelines.
The Uruguay international, who arrived at St Mary's from Bologna for 12 million pounds in August, missed Southampton's 2-2 draw with Fulham on Oct. 7 after suffering a dead leg in training.
The 21-year-old has been ruled out of Southampton's trip to West Ham on Saturday by manager Nigel Adkins, who also confirmed the dead leg resulted in the swelling of the midfielder's thigh.
"I think six weeks is probably about right, but we'll see how he progresses through the rehab stages," Adkins told reporters. "If the time is from the medical department, it is from the date of original injury. He is showing good signs of recovery at this moment of time, but he won't be fit for the weekend."
Follow GOAL.COM USA on