Adios Mendi?
The 32-year-old former Spain international has struggled to make his mark during three years with Boro and has been linked with a return home to join Athletic Bilbao.
Mendieta has only featured seven times this season and hasn't played at all since the end of September.
Boro manager Gareth Southgate said: "I understand his frustrations at not being involved.
"As a senior player if he is not going to be part of the first team, we have to look to see if we can help him in some way. But I don't think I can give him the games he wants.
"At his age, I am sure he will want regular first-team football.
"There will be a few clubs alerted to the fact he's not getting a place and we'll see what happens."