Manchester United defender Phil Jones will be sidelined for at least three weeks with "mild thrombosis".
The 23-year-old England defender missed Saturday's opening-day 1-0 Premier League victory over Tottenham at Old Trafford.
He was part of United's pre-season tour of the United States and trained in Manchester this week.
Thrombosis is the formation of clotting of the blood in a part of the circulatory system.
Jones, who has won 17 England caps, began his career at Blackburn before joining United in 2011.