Ross County midfielder Ben Paton has been dealt a major blow after being sidelined for the bulk of 2023 with a torn cruciate ligament.
Midfielder Paton suffered the injury in training last week, before undergoing a scan on Monday to determine the damage.
The setback confirms the fears which Mackay had suspected prior to the scan.
Canadian Paton, who has made 11 appearances this term, is due to be out of contract at Victoria Park this summer.
Mackay insists Paton will continue to be paid beyond that, with no decision to be taken on his future until he is back to full fitness.
The Staggies boss said: “Ben has torn his cruciate, which is what we thought.
“We’re devastated for the boy. He’s a great lad, and he’s going to have a long time in front of him now.
“We’ll deal with his contract, there’s no way that we’ll just let that expire.
“All the way through his recovery, he won’t be judged until he’s fully fit again and he will be getting paid by the club until he’s fully fit.
“It’s something that myself, Steven Ferguson and Roy MacGregor spoke about once we had spoken to the physios and to Ben, and I’ve assured him of that.
“It means he can just concentrate on his recovery, because that will be nine months and he was due to be out of contract in five.”
Mackay keen to reassure Paton
Paton’s setback comes at a time when striker Alex Samuel is returning to the squad, having suffered the same injury last February.
Mackay, who suffered a cruciate injury during the early stages of his playing career at Celtic, is keen to reassure the 22-year-old that he can recover from the blow.
He added: “Any time I see the word ‘cruciate’ on the telly I despair.
“What I did say to Ben the other day was that I got one at the same age as him, and I played until I was 36 and it never gave me a problem for the rest of my career.
“It’s dreadful news, and it’s a long term one, but it’s absolutely fixable.
“I did it, and I played for 15 more years with no problems with it.
“It’s not like something that’s called an osteochondral defect in the knee where’s there’s a hole in the knee. You can’t fix that, you just have to manage that for the rest of your days and it swells after games and training.
“A cruciate can be fixed, and it will be stronger than the other knee when it was fixed.
“Whenever I see it, I despair because it’s the next nine months of their life. You start thinking about your career, wondering if you are finished, and it’s so innocuous when it happens.
“It’s not caused by a heavy tackle, it’s a twist.”
Staggies boss still looking to strengthen squad
Mackay remains on the lookout for at least two more additions to his squad before the transfer deadline.
His only January addition so far is midfielder Nohan Kenneh, who has joined on loan from Hibernian.
The Staggies have lost Callum Johnson, who joined Mansfield Town for an undisclosed fee, however Mackay insists right back is not a priority position.
Mackay added: “I’ve got Keith Watson there, and young Dylan (Smith) – as much as he’s a youngster – has trained really well with us and has been on the pitch already.
“What I don’t want to do is take someone in who won’t play for six months, because Connor Randall has been Mr Steady since the day I got here.
“He was just coming into a great vein of form when he took the injury, but we’ve got Keith that can cover and young Dylan that can come in.
“Victor Loturi can play there as well, he has before, so I’m more interested in trying to do something in the attacking area of the pitch.”