The ex-Celtic captain slaughtered Grant, who was No2 to Tony Mowbray, as he called out his man management and revealed he would have left Glasgow to move down south if he had remained on the coaching staff.
As it turned out, Neil Lennon turned things round at Celtic after replacing Mowbray with Grant also leaving the club.
Brown had received offers from Tottenham Hotspur and Newcastle while at Celtic but rejected the chance to move to the Premier League.
However, in a scathing verdict on the former Scotland coach, Brown revealed he has no time for Grant.
Speaking on Open Goal, he said: “Lenny came in and we started winning games and the momentum changed from when Tony was there.
“I think if Tony and Peter Grant were still there, I’d have been away straight away.
“I had no time for Peter Grant whatsoever.”
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On the key issues he had with Grant, Brown said: “Man management. Personal.
“Personality? Zero.
“Tony, I got on alright. But Peter Grant, no.”
Detailing transfer interest from down south during his playing career, Brown added: “After my second season at Celtic I got offered the chance to go down to Spurs. They put in a bid.
“Then just before Lenny came in, at the end of my first contract, Newcastle offered me a five-year deal to go down there.
“Imagine me, I’m bad enough in Glasgow, imagine how many nights out I’d have in Newcastle!”
