Juan Mata is upset with the way Victor Valdes has been treated at Manchester United.
Valdes, 33, has been axed from Manchester United's first team and excluded from their official team photo while he is being forced to train away from Louis van Gaal's squad.
"It's a shame what is happening with him, as he is a great goalkeeper," Mata told Marca.
"He wants to compete and has proved himself as a goalkeeper."
Mata also refused to divulge details of their falling out.
He added: "I don't know what happened between him and Van Gaal; that is something, only they can say."