The Portuguese boss has come in for criticism in certain circles for his way of playing of late, and he publicly admonished Eden Hazard for the Belgium winger's refusal to track back in his Friday press conference.
Merson has suggested that Mourinho's style would not be attractive to potential signings.
He told Sky Sports News: "He's asking Oscar to work hard, and [Mourinho] needs to be careful. The lad can play but by the time he gets it, he's too tired.
"If I was a player with that amount of flair and you told me to go to Chelsea, I'd say 'well, not really'. I'd want to be playing further forward, that's my job."
Chelsea are currently second in the Premier League.