Ronaldo, 37, returned to United last summer following a £13.5 million move from Juventus. The Portuguese star managed 24 goals in 39 appearances for the Red Devils but was part of a woeful United side.
The thirteen-time Premier League winners floundered to a sixth-place finish in the league and ended the season without a trophy.
The Portuguese had previously spoken of his excitement of working with Erik ten Hag following the Dutch coach's appointment in May. However, La Repubblica (via GetFootballNewsItaly) reports that all is not well in Ronaldo's camp with regard to his role in Erik ten Hag's project.
Ronaldo reportedly still has reservations over the Red Devils' lack of UEFA Champions League football next season. The Portuguese star's agent Jorge Mendes is said to be looking for a new club for the striker, with AS Roma emerging as a potential suitor.
Led by Ronaldo's former Real Madrid manager Jose Mourinho, Roma can make the most of tax reductions due to the 37-year-old's prior stint at Juventus. The report claims:
"Jorge Mendes has an open preferential lane with those at Trigoria: after Mourinho, he also brought Rui Patricio and Sergio Oliveira, and with compatriot Tiago Pinto, he has an excellent relationship since his time at Benfica.
Ronaldo reportedly may have doubts over joining Roma with the Italian side not playing Champions League football next season. His former side Sporting CP are also being touted as a potential destination. The Primeira Liga club's president Frederico Varandas is believed to be trying to fix relations with Mendes.
Sporting CP can offer Ronaldo Champions League football next season following their second-place finish in the Primeira Liga.
Will Cristiano Ronaldo leave Manchester United?
Cristiano Ronaldo was one of few positives at Old Trafford this past season, operating as United's sole savior countless times. His blockbuster return to the Red Devils last summer was heralded by many as the catalyst for the side to bring back the glory days of the club.
However, Manchester United slumbered, both domestically and in Europe, with only Ronaldo's goals sending them to sixth in the league.
The Portuguese star is not familiar with missing out on Champions League football and this looks to be proving problematic for Manchester United.
It would be hasty, though, for Cristiano Ronaldo to deem himself not a part of Erik ten Hag's project given that the pre-season is yet to kick off.