Riemer referred to an incident last week where Uniteds new Danish winger Patrick Dorgu was sent off against Ipswich and Roben Amorim chose to to take off Alejandro Garnacho for Noussair Mazraoui to bolster his defensive ranks with a one-man-disadvantage.
The visibly upset Garnacho then chose to storm down the tunnel before the half was even finished much to the displeasure of the Old Trafford crowd and Amorim in particular. Riemer is also very critical of the way Garnacho behaved in the wake of the red card for Dorgu.
Riemer, who will select his squad for the upcoming Nations League fixtures against Portugal on Tuesday, made it clear that he will confront players who put themselves above the team. It can be those who express their disagreement with a substitution or complain about a lack of playing time.
"If I'm deeply dissatisfied with a player, I won't tell the media. I will tell him that myself afterwards, and just as well if a player thinks I've made a mistake in relation to a substitution, you don't air your dirty laundry in public."
Riemer and Denmark will face Portugal on 20 March in the Nations League quarter-final.