The playmaker has turned out 10 times for the Red Devils in all competitions this season, but he boasts just two assists from four Premier League starts on the right-hand side.
Mata's current deal is due to expire in June but United can trigger a one-year extension, although Solskjaer has confirmed that no decision has been reached yet.
Speaking at a press conference ahead of Man United's Premier League clash with Fulham, Solskjaer said: "The decision is very difficult every time with Juan. You know he has the quality. If he plays, he scores goals, he has contributed this season.
"Then again, you have other players who have taken his role as well. Mason [Greenwood] has done well in that position and Paul [Pogba] now.
"Juan really contributes in and around the group. He is one of those I have discussions with all the time and it is difficult to leave him out but unfortunately that's where it is at the moment. No decision has been made yet."
Mata has chalked up 50 goals and 47 assists in 265 appearances for the Red Devils, where he has won one Europa League, one FA Cup and one EFL Cup since arriving from Chelsea in 2014. body check tags ::