PFA chief Gordon Taylor has urged Roberto Mancini and Carlos Tevez to sit down and sort out their issues.
The Argentine striker allegedly refused to come off the substitutes bench during City's 2-0 defeat to Bayern Munich on Wednesday night, a claim the player has since refuted.
"There have been mixed messages for some time," Taylor told BBC Radio 5 Live.
"They are human beings and emotions run high, but clearly things aren't right.
"They've got to get round the table and sort it out, it's unsatisfactory at the moment. It's happened before with players. The two have contrasting temperaments."
City next face a trip to meet Blackburn Rovers in the Premier League on Saturday.
