Hearts head coach Robbie Neilson fears he could lose full-back Callum Paterson's for six to eight weeks with a knee injury.
Goals from Billy King, Osman Sow and Paterson helped Hearts beat Annan 3-1 in the Petrofac Training Cup but the latter had to helped from the field on a stretcher having appeared to have twisted his knee.
“He has his leg in a brace and the physio is saying we’ll need to get it scanned on Monday,” said Neilson.
“You can’t tell with these things until you get them scanned. I think he got a shock and these things are painful, but, hopefully, it’s just a six-to-eight week job – that’s probably the most positive outlook. He just got his studs caught in the grass, and maybe hurt his medial ligament.
"It takes the shine off the day a bit, and it's obviously disappointing but gives others opportunities. Liam Smith is someone we're looking to push on this season, Jordan McGhee can play there too, so we have a few options in that area.
"We created lots of chances, the boys were getting into great positions. I thought the two wingers did really well, Osman gave us a lot up top too. So far he's been great, he's still getting fit. he has a long way to go yet, but he has pace and power, and he'll be really important for us this season."
Paterson suffered ligament damage in training in January 2013, an injury that ruled him for the remainder of that season. He cemented his place in the affections of the club's support by scoring both goals in a 2-1 win over Hibernian in April this year.