The Newcastle boss recently underwent a triple heart bypass operation and will require a lengthy spell away from the game as he seeks to make a full recovery.
Kinnear had complained of feeling unwell prior to the Magpies' clash with West Brom on 7th February.
He was immediately taken to hospital, where the full extent of his problem was revealed.
Having gone under the knife last Friday it is expected that he will need around eight weeks of rehabilitation before returning to full health.
The heart scare is unlikely to keep him away from football for long, though, as he has already bounced back from a similar problem he suffered in 1999.
Kinnear, who was in charge of Wimbledon at the time, collapsed prior to a Premier League fixture with Sheffield Wednesday in March of that year.
Positive personHarford was among the Dons' coaching staff that day and has backed his former mentor to be back on the sidelines at St James' Park before too long.
"I absolutely feel for him," the Luton boss told Sky Sports News.
"I have left a couple of messages on his mobile phone but I haven't got back to him yet. I'd like to get up and see him but I haven't had the opportunity to.
"I send him my best wishes. He will be fighting.
"I was with him the first time he had a scare at Sheffield Wednesday and he came back from that.
"He's a very positive person, he changed his lifestyle and I know 100 per cent that he will want to stay in football. I wish him all the best."