Diogo Dalot has been the preferred right-back for Rangnick, even when £50million-man Wan-Bissaka has been available.
Wan-Bissaka has been in United training this week ahead of Friday's FA Cup fourth round clash at home to Middlesbrough.
But it appears there has been a number of sessions he has not been a part of.
Speaking on the Transfer Window podcast, Duncan Castles claims Wan-Bissaka has been absent on numerous occasions.
The 24-year-old took the "unusual" step of calling in sick instead of visiting the training ground to be assessed by medical staff.
Castles says United have punished Wan-Bissaka for his behaviour.
"My information is that he has missed a lot of training sessions," Castles said.
"I'm told that on at least one occasion he failed to turn up to training, citing illness as a reason, calling in to say that he was ill and that's why he wasn't coming in for training.