Western Sydney Wanderers have come under scrutiny over the treatment of their players from the A-League players' union, which has criticised the club for ostracising four members of the senior team told they no longer had a future at Parramatta.

The Wanderers are alleged to have isolated four players from training sessions in recent weeks and encouraged them to sign mutual contract terminations during the January transfer window.

Fairfax Media understands Kwabena Appiah, Vitor Saba, Daniel Mullen and Seyi Adeleke spent about a month training away from the rest of the squad and were excluded from other activities after being told they would not play first team football this season.

Sources close to the club say the quartet would go through the usual warm-ups with the rest of the squad before training in isolation with an assistant coach where they would undergo light drills that had no relevance to tactics or match preparation.