Manager Stanley Menzo reportedly ordered Watt off the training ground after the teenager refused to comply with training ground instructions.
Menzo sent the striker home last month after a row over plans to play Watt on the wing.
The 19-year-old striker, who famously scored Celtic’s second goal in their 2-1 win against Barcelona 12 months ago, has been involved in several run-ins with his new manager since his transfer deadline day move.
Menzo branded Watt unfit when he first arrived in Belgium.
Menzo said at the time: “I see him as the type who thinks by doing a little bit he can get a lot. I think that is wrong. I told him by doing more he can be a much better player.”
Watt scored in the game which followed his manager’s comments, and celebrated by taking off his shirt. Watt said: “I just wanted to show that I am not fat. I knew perfectly well that if I took my top off I would get a yellow card – it happens all over the world.
“But I just wanted to show everyone that I am in prime condition.”
Watt has played six games for Lierse, and was controversially sent off for violent conduct less than a minute after being brought on as a substitute in a game against Charleroi.