U.S. international Lynden Gooch will miss between two and three months for Sunderland with an ankle injury, manager David Moyes said on Friday.
Gooch left the Black Cats' under-23 game on a stretcher on Monday, and Moyes confirmed that the midfielder appears to have suffered ligament damge.
"Unfortunately, Lynden Gooch was stretchered off in the reserve game against Tottenham in midweek," he said. "It looks like damage to one of his ankle ligaments.
"He's away to see the specialist today, and then we will find out whether or not he will need an operation.
"But he will probably be out for somewhere between eight and 12 weeks, depending on exactly what the surgeon says."
Gooch has been a surprise fixture in the Sunderland lineup this season, appearing in nine league games and three cup ties, and Moyes called the injury "a terrible blow for Lynden."
"We really like him, he's infectious and he's a good character," the manager said. "I spoke to him a few weeks ago and said I thought his levels had just dipped a little, but that would be normal for a young player when you think of the games we asked him to play in and the position the team had been in.
"But in the last week or so he had started to look fresher in training, and the injury is a real blow for him and for us."
Gooch, 20, made his international debut for the U.S. against New Zealand in October and was officially cap-tied - meaning he cannot represent another FIFA-affiliated national team -- in the World Cup qualifying defeat to Costa Rica.
While the injury is likely to prevent him from joining up with the U.S. for Bruce Arena's first training camp in January, Gooch should be fit in time for the World Cup qualifiers against Honduras and Panama in late March.
Moyes also said Jan Kirchhoff would return for Sunderland to face Leicester on Saturday, while Jack Rodwell is still a few weeks from his return from a hamstring injury.