Former Manchester United captain Roy Keane has suggested that Chris Smalling needs to improve further if he is to be a key part of the team's defence.

The England centre-back has been widely regarded by pundits as one of the most improved players this season for both club and country.

However, Keane has said that Smalling, along with Daley Blind and Phil Jones, are yet to convince him that they are good enough to play in United's back four.

"As long as Blind and even Smalling - I'm not sure about him - or even Jones, are playing at centre-half, particularly in the Champions League against the bigger teams, United will get ripped apart," Keane told ITV Sport.

"He's still okay. I still think he gives you a chance and he's come on, but he's got a long way to go yet for me."

Smalling played in United's 2-1 defeat to PSV Eindhoven on Tuesday.