The Tangerines host the Hoops at Tannadice Park on Sunday and although Flood is well aware his old club have got their season back on track, he is not about to go in half-hearted against his ex-colleagues.
"Celtic have come back strongly in the league in the past month or so," he said.
"They had a sticky patch but I had no doubt Neil Lennon would turn things around.
"They've had a few injuries to key players and Scott Brown was a big miss.
"I've not spoken with him this week. I'll just stay quiet and have a word after the game.
"I still have friends at Celtic but that won't mean anything when the game starts."