Callum Paterson: Hearts right-back sidelined for six to nine months
Hearts and Scotland right-back Callum Paterson is facing a lay-off of between six and 10 months after a scan showed serious damage to his left knee.
Paterson was injured in Tuesday's 4-0 win over Kilmarnock at Tynecastle.
The 22-year-old was taken off on a stretcher after 15 minutes, shortly after scoring his side's opening goal.
Paterson, who is out of contract this summer, said on Twitter: "Absolutely gutted with the scan results. But these things happen in life. I will be back."
The defender, capped five times for Scotland, looked certain to move to England either in January or at the end of the season.
Hearts director of football Craig Levein said earlier this month the club would only consider selling Paterson for a "seven-figure sum".
Should the Scotland international leave Tynecastle in the summer, Hearts would be due a development fee of around £450,000.
But that fee will not apply to any cross-border move after Paterson turns 23 in October.
Hearts head coach Ian Cathro told the club's website: "It's a bad one for Callum and everyone here is gutted for him.
"There was real concern for him last night and unfortunately that concern has been compounded with the news that he could be out for up to 10 months.
"Callum's a top-class player and we'll miss him in the first team, but we now have to look to those within the squad to step up and fill the void.
"We'll help Callum as much as we can though this difficult time."
The loss of Paterson, who is Hearts' joint top scorer this season with 10 goals, will also be felt by Scotland head coach Gordon Strachan.
Aston Villa's Alan Hutton retired from international football in October soon after being displaced as Strachan's first choice.
Head coach Ian Cathro, speaking before he learned the results of the scan, said: "He has been here since he was 16 and has grown into a good level footballer.
"He has grown into a strong man, a strong character and an important personality for everybody here. I couldn't speak more positively of him in the short period of time I have worked with him."
It is not the first time Paterson has had injury problems to contend with.
He suffered a shoulder ligament injury in a win over Kilmarnock in February that kept him out of action for nearly two months.
Paterson required surgery to repair medial ligament damage in his left knee, sustained in a Challenge Cup win over Annan Athletic in July 2014, that also ruled him out for two months.
In February 2013, he tore a ligament in his foot during training that kept him out for the remainder of the season.
Cathro said Paterson will recover from his latest setback and continue to progress his career.
"Callum will be able to achieve what he wants to achieve in the game," he said. "Irrespective of whether there is good or bad news, he will be able to go to those places.
"If there is a road bump, he will deal with that and have support to deal with that."
Head coach Cathro said he "expects to do some business" in January as he bids to "evolve the squad in how it is balanced and find players that can improve us".
That is likely to include some players who have not featured in the first four games of his tenure leaving Tynecastle.
"We would be supportive of players looking at opportunities which involved them being able to play, if the opportunities are limited here," he added.
There was better news for Hearts on midfielder Don Cowie, who was carried off with a neck injury and taken to hospital during a 3-2 defeat by Dundee last Friday.
However, he could face Aberdeen on Friday having recovered from the injury and a subsequent illness.