The Red Devils host Brighton at Old Trafford at 2pm on Sunday to begin the Erik ten Hag era.
It would have been a tough decision for the new United boss to make after Ronaldo's well publicised desire to leave.
The 37-year-old has missed the majority of their pre-season season, not travelling on their tour of Thailand and Australia due to 'family reasons'.
When the team did return, he held showdown talks that involved in agent, Jorge Mendes, and members of the clubs hierarchy.
He again reiterated his desire to leave, but still remains a United player.
The five-time Ballon d'Or winner is keen to play in the Champions League this season, however, the list of potential destinations has dwindled with the likes of Bayern Munich and Chelsea ruling themselves out.
Ronaldo has featured once in pre-season for the Red Devils, in a friendly against Rayo Vallecano, but came under fire for leaving at half-time.
Ronaldo was among a number of players that left the Rayo friendly early - something the manager told a Dutch broadcaster was 'unacceptable' by those involved.
"Now I have to point - those who left but there were many players who left, but the spotlight is on Cristiano and that is not right," Ten Hag said.
"So I think then do your research and make out many players left, that was what was said.
"Good, but I don't understand what is the relation. He was part of it. Again, there were a lot of players."
Asked about Ronaldo's position at the club, Ten Hag said: "I'm really happy.
"I told you before, we plan with the season (with him). We have a top striker and I'm really happy he's here, he's in the squad and we stick to that plan."
While Ronaldo was on the bench, Ten Hag handed debuts to Christian Eriksen and Lisandro Martinez.
On his team selections, the Red Devils boss said: "Ronaldo is working really hard to get in the right fitness levels, it will take time.
"He started pre-season last week. It depends on how quick he is progressing.
"We should act as a team, I want to see a team performance. Every game, that is the most important. Football is a team sport."
Man Utd: de Gea, Dalot, Maguire, Martinez, Shaw, McTominay,
Fred, Sancho, Eriksen, Bruno Fernandes, Rashford. Subs: Ronaldo,
Malacia, Varane, Heaton, Wan-Bissaka, van de Beek, Elanga,
Garner, Garnacho.
Brighton: Sanchez, Veltman, Dunk, Webster, March, Lallana,
Caicedo, Trossard, Gross, Mac Allister, Welbeck. Subs: Lamptey,
Colwill, Mwepu, Maupay, Sarmiento, Undav, Mitoma, Steele,
van Hecke.