Middlesbrough have revealed that centre-back Ben Gibson could miss the club's opening game of the Championship season at Preston North End.
The 22-year-old picked up a hamstring twinge during his first pre-season outing of the summer against Barnsley after representing England Under-21s in the U21 Euro tournament earlier this summer.
Boro said that Gibson would be out for around seven to 10 days, which could rule him out of the trip to Preston a week on Saturday.
"It's very frustrating," Gibson told the club website. "I felt really good, the plan was to play 45 but I felt that good I was going to ask to stay on longer.
"But thankfully it's not a bad one, just very frustrating."
Gibson made 39 Championship appearances last term as Boro reached the playoff final and were denied promotion to the Premier League by Norwich City.