United were said to have concerns about Ronaldo’s behaviour and may consider terminating his deal, Sky Sports claimed.
Cristiano Ronaldo has been asked to change his attitude by the club.
Ronaldo, 37, stormed off the pitch after United’s 4-0 defeat to Brentford without shaking Erik ten Hag’s hand.
The Portuguese also slammed David De Gea after his two errors allowed the Bees to take a 2-0 lead.
Ronaldo was filmed waving his arms and gesticulating towards the Spanish keeper.
After the full-time whistle Ronaldo failed to applaud the travelling fans and exchanged what seemed curt words with coach Steve McClaren before quickly heading off the pitch.
However United are not said to be considering letting him go over his behaviour.
Ronaldo has reportedly asked to leave the club this summer and he sat down for showdown talks with Ten Hag and agent Jorge Mendes when he returned to Carrington last month.
The striker wishes to play Champions League football but a transfer has not materialised.
Ronaldo was offered to AC Milan and their rivals Inter but both clubs rejected the opportunity to sign the superstar.
Reported interest from Atletico Madrid and Sporting Lisbon has also not produced a move, leaving Ronaldo short of options.