The 34-year-old actor, who is in his second season on the CBS sitcom, has grown increasingly surly as the show's ratings slide, reported Showbizspy.
"When Ashton joined the cast, he was like a breath of fresh air. He was seen as the show's saviour, and everyone rallied around him. But it is pretty clear Ashton is not as enthused about Men as he was last season. Some people are even calling him 'Charlie Jr' behind his back," a source said.
Kutcher, who is now dating his former 'That 70s Show' costar Mila Kunis, is also said to be unhappy that he is only getting USD 700,000 per episode, not the USD 1 million he wanted.
"Ashton feels he is being under-valued. At this point, I think it is doubtful that he will return next season," the source added.
