The striker endured mixed fortunes on loan at SK Lierse last season as he got caught up in a number of public spats with eccentric boss Stanley Menzo, who accused him of being unfit and lazy.
The 20-year-old netted nine times on the Continent and now has a chance to kickstart his career under new boss Ronny Deila.
Watt told Scotzine: "To be fair, I don't really want to talk about him now. He means nothing to me now.
"He is an ex-manager and that's all he'll ever be.
"I'll never play in another team managed by him. I'll never put up with him again.
"He came out and said a lot of times that I did this and that wrong, but I was always scoring, I always scored goals for him.
"Some would say that I helped him out, but it was his choice.
"Everything I came out and said in the press was gospel truth, it was all true. I'm not going to say anything bad about him.
"I'm not going to come out and badmouth him because it would be childish of me, I feel as if I'm better than that, I'm not going to come out and slaughter a guy.
"I know he gave me a hard time, but that's it. It's finished now.
"The boys were all good, they had meetings asking the assistant coach to play me, give me a chance.
"If it wasn't for some of them then maybe I would have lost the head and maybe I'd have tried to get home early, but they helped keep my feet on the ground and keep my head in the right place."