Watt was branded "lazy and unfit" by his coach at SK Lierse, Stanley Menzo, after he scored on his debut in September. He was reported to have been sent home from training on two separate occasions and there was talk of him returning to Celtic Park in January.
The 20-year-old appears to have knuckled down and has scored seven goals in eight games for Lierse but was left out of Stark's squad for a third successive time ahead of tomorrow's friendly against Hungary at Tannadice.
That prompted Watt to tweet: "Thought it would be 3rd time lucky for Scotland squad £piedagain."
Stark confirmed that Dundee United duo Ryan Gauld (hip) and John Souttar (Achilles) are out and are set to be joined by St Johnstone striker Stevie May (hamstring) but only the Celtic midfielder John Heron has been drafted in.
On Watt, Stark, the Scotland head coach, said: "He just said he was disappointed, basically, and he used a modern term, I'm told.
"It is good that Tony is keeping a close eye on it because I am keeping a close eye on him and we are waiting for the right time to introduce him again, when he shows that he has matured a wee bit over in Belgium.
"Tony is over there, by Neil Lennon's admission, to progress as a player and a person so I don't feel any difference in terms of Tony scoring over there. I knew he would, I would have probably put money on it.
"There is no greater admirer than me of his ability - he is strong, quick and a terrific finisher - but I spoke to Tony after the first time I left him out and explained things. He knows where we are."