Rangnick is in interim charge of the Red Devils, until the end of the season, but there has not been an immediate improvement in their form.
The last two matches, a draw with Newcastle and defeat to Wolves, were particularly concerning for the below par performances.
Reports claim there is a rift in the dressing room at Old Trafford with as many as 11 stars wanting out of the club.
Former Chelsea man and talkSPORT host Jason Cundy believes the Man United squad have no confidence in the manager.
"You can tell they don't believe in the manager," Cundy told The Sports Bar. "In my experience, players have never gone out not to try.
"What you do have is a lack of belief in the manager and lack of belief in what he is trying to achieve.
"That can spread very quickly, not just through the team but to the dressing room. They will be talking.
"[They were] two different sides. Wolves under Bruno Lage are well coached and know exactly what he's doing. Okay, they are not the most exciting side in the world, but they totally bossed the game.
"Wolves bossed Man United at Old Trafford. It should have been more than 1-0.
"You look at those two teams [against Wolves] and one team believed their manager. It isn't just Rangnick's fault."
Cundy also believes that United will be kicking themselves for deciding against going after Antonio Conte.
Conte was hired by Tottenham at the start of November, just weeks before Ole Gunnar Solskjaer was sacked.
The Red Devils' decision to give Solskjaer more time before finally axing him allowed the Italian to slip through their fingers.
Cundy added: "One of the mistakes that Man United made is how they let Antonio Conte slip through their fingers when he was there.
"The answer was there and in front of them. He was out of work. It was there. Credit to Spurs, they rectified their mistake and got the job done."