Angry for no reason (?)

I coach Mallorca and I've signed Masoud from Osasuna along with a few other players. A few days after signing (around late July) he said he was worried because there is to much competition for a spot in my starting eleven, I promised him he was my first choice and the problem seemed solved. On early september he becomes unhappy because I didn't keep my promise, which makes no sense as I had put him on the starting eleven on all pre-season matches and on the only two season matches played. Whats wrong with this guy?! Ay one had a similar problem?