United haven't been at their best in the Premier League, putting in derisory performances against arch-rivals Liverpool and Manchester City.
Despite this, boss Ole Gunnar Solskjaer has largely stuck with the same squad, leaving the likes of Donny van de Beek and Jesse Lingard out in the cold.
This has led to the likes of van de Beek and Lingard reportedly asking to move on in January, while the latter has dropped a big hint on where his future might lay.
And former Arsenal defender, Keown, insists that the Norwegian must utilise his squad more - or risk being sacked.
He told talkSPORT: "When they're winning games, I think it's easier to look at the likes of [Alex] Telles, and [Donny] van de Beek, and [Juan] Mata, and [Phil] Jones, and to say, 'Okay, we're not picking you because we're winning games.'
"But now that dressing room must be interested in what's happening on the inside because there will be a lot of anger, nobody is getting any joy out of this.
"The 11 he picks isn't winning and the squad, as well, are not getting any reward.
"There now has to be some changes to the personnel. Or, ultimately, they change the manager."
United face Watford on Saturday and, after a run of six defeats in 12 games, Solskjaer is keen to turn things around, as he comes under increasing pressure at Old Trafford.
And he has reportedly held talks with some of his key players, including Cristiano Ronaldo, captain Harry Maguire, and Bruno Fernandes, on Thursday as he attempts to get the club back on track.
The Daily Mail are reporting that Luke Shaw, Victor Lindelof, and Nemanja Matic were also involved in the meeting, which took place at the club's training ground.