Hearts could be without Michael Smith for up to six weeks after boss Craig Levein confirmed the defender had suffered a thigh tear during the 4-0 Scottish Cup victory against Auchinleck Talbot.
The Northern Ireland international will be sent for a scan on Monday to ascertain the severity of the setback, but Levein is braced for bad news.
Levein said: "The big downside was Mick. He was as professional as ever today and his performance was very good. But he's torn his thigh muscle and he will be getting scanned on Monday.
"We don't know how long he will be out. It depends how bad it is – whether it is a grade 1, 2 or 3. But it could be six weeks out.
"It was his standing leg when he passed the ball."
Levein, who has welcomed Christophe Berra, John Souttar, Steven Naismith and Uche Ikpeazu back from serious injuries in recent months, smiled ruefully and said: "We are obviously not allowed to have them all fit, are we?"
Smith's injury put a dampener on an otherwise satisfactory afternoon for Levein, who watched his side book their place in the quarter-final draw courtesy of goals from Berra, Demi Mitchell, Steven MacLean and a maiden senior goal from youngster Aidan Keena.
Levein continued: "It was a bit of a no-win situation for us, but I was pleased with our first-half performance.
"We didn't quite play at the same intensity in the second half. We stopped playing the easy balls and tried to do something more difficult – but it didn't cost us and we are through."
Meanwhile, Auchinleck manager Tommy Sloan insists a memorable Scottish Cup adventure has only served to whet his appetite to return to this stage.
Sloan's troops claimed a famous victory over Ayr United in the fourth round before coming up short in Gorgie and, despite conceding there was a 'gulf' between the teams, he lapped up the occasion.
He added: "It's strange but even in the first half, when we were taking a bit of a doing, I was still enjoying being here.
"We've had great times from the moment the draw was first made in July and we've gone a round further than we've ever done before.
"This is what we want to be doing, where we want to be playing. I hope the boys take the positives of this into the other competitions we'll play this season.
"Hopefully, we'll be back in this competition next year and we can go on a run again."
