Hearts fear midfielder Scott Robinson fractured his shin in the club's friendly against Dinamo Bucharest on Sunday.
The 22-year-old was carried off during the first half of the match, which the Tynecastle side won 2-1.
And the club said it was thought he had a "possible fracture on his shin."
Hearts included former Dundee United midfielder Prince Buaben and ex-Berwick midfielder Lee Currie in their squad as trialists against the Romanians.
Gary Oliver and Sam Nicholson scored the goals for the Scottish Championship side.
Dinamo Bucharest finished the game with 10 men after having a player sent off during the first half.