The 30-year-old spent last season on loan at Roma, where he rediscovered his best form.
Smalling is now back at Old Trafford, but with United keen to offload him before the transfer window shuts on October 5, he has been frozen out and is training alone.
The Red Devils are believed to be holding out for £18 million and boss Ole Gunnar Solskjaer admitted earlier this week that the club have not yet received any offers ‘up to the level’ that they want.
United’s defensive frailties were exposed in their 3-1 loss to Crystal Palace in their season opener, with Victor Lindelof in particular struggling to deal with Roy Hodgson’s side’s pace in attack.
Keown says that after an impressive season in Italy, Smalling deserves another shot and admits he may even be a better defender than first-team regular Lindelof.
‘I just feel that Chris Smalling should be given an opportunity,’ Keown told talkSPORT. ‘I look at Lindelof and feel maybe Smalling is a better player.
‘But it seems as if a decision has been made for Smalling to leave already. I’m not sure Lindelof could’ve gone to Roma and performed in the way that Smalling has.
‘At the moment, they’re trying to get him out as they’re trying to get Sancho in perhaps from Dortmund.
‘He’s just a pawn in all of this game and when that game’s over and the transfer window finishes, if he’s available, he comes back into the thinking of the manager.
‘But for now he’s not going to play and it’s a shame, but along with Phil Jones, [he’s] another they seem to have given up on.