Hearts manager Craig Levein fears John Souttar may need hip surgery after being forced to withdraw from the Scotland squad.
The defender is struggling with an injury affecting his hip and hamstring which has denied him a first senior international cap.
He was named in national coach Alex McLeish's squad for forthcoming friendlies away to Peru and Mexico but has now withdrawn. Celtic midfielder Stuart Armstrong has also pulled out due to a hamstring complaint with McLeish and his players meeting up in London on Wednesday.
Souttar sat out Hearts' final two league matches of the season with the problem but was desperate to travel across the Atlantic in the hope of making his Scotland debut.
Levein admitted the injury is worse than first thought and explained his concern that an operation may be needed to cure it.
"We've had a scare with John because this injury is a little worse than we feared. I'm hoping it settles down and doesn't require any surgery," Levein explained to the Evening News.
"It was a really weird injury he got against Celtic. He was clearing the ball across his body and someone came in and caught him on the hip join. It was a right clatter. I'm still not 100 per cent sure whether it's just muscular or if there's some damage to the cartilage in the hip. That would a bigger problem for us.
"If it's just muscular and it clears up quickly, then we're fine. If it's worse than that then it would have longer-term implications."