The Frenchman hasn’t featured under Jose Mourinho in the club’s last two games against Feyenoord in the Europa League and West Ham United in the Premier League.
Mourinho recently explained his exclusion is a result of other players moving ahead of Martial in the pecking order and not because he is injured.
Redknapp has warned Mourinho that letting Martial go could end up as another huge mistake for Man United.
He said: “Martial is on the bench and if United let him go he could be another De Bruyne, a Lukaku or a Mata.”
Mourinho sold Romelu Lukaku, Kevin De Bruyne and Juan Mata while in charge of Chelsea and they have all gone on to become a huge success away from Stamford Brdige.
Man United have had their fair share of transfer disasters too, Pogba’s notably the most expensive of them all, after he left the club on a free transfer and returned for a world-record fee.
Martial has proven his importance to the club under Louis van Gaal and letting him go after a rough patch would be a terrible decision, his talent is beyond his years and I would hate to see him leaving Old Trafford as he hasn’t reached his true potential.