Hoops teenager Watt came off the bench to score on his debut in a 2-0 win over Kortrijk on Sunday.
But Lierse gaffer Stanley Menzo was still scathing about the 19-year-old's physical shape and attitude after the game.
Lennon is hopeful the player, who scored the winner against Spanish cracks Barcelona last season, will improve as a result of the experience in Belgium.
He said: "I'm surprised the manager made his thoughts public, but physical conditioning is part of his game that he does need to work on.
"He has gone there to play and I'm pleased that he has come on and scored. He has got that in his game. But there are aspects of his make-up that he needs to work on. Obviously, the Lierse manager has told him that.
"Put it this way, he prefers to play the football than do the physical side of things at times. But he's 19. He has to learn that to be a top, top player you need to put the work in as well as the talent.
"I think he will learn. You are hoping that he will come back a better player from this.
"Tony has plenty of time in his career, but I think enough people have told him now. He knows what is required of him and the ball is firmly in Tony's court.
"Listen, I have had plenty of conversations with Tony. I am pleased for him that he has scored and he is playing in a different environment. That might be good for him as well, to get away from the goldfish bowl for a bit.
"I will give him a call in the next couple of weeks and see how he has settled in. He has only been gone for a couple of weeks."