The Portuguese superstar was absent as Ralf Rangnick and 21 players met at the Lowry Hotel for their pre-match routine.
Edinson Cavani, Raphael Varane and Luke Shaw were also missing as United players entered the plush Manchester city center hotel to prepare for Sunday’s Premier League clash with City.
Ronaldo was seen taking part in a full training session on Wednesday.
The Portuguese superstar is reportedly injury-free in the sessions since then.
And United fans will be praying he can line up in the unmissable derby showdown at the Etihad.
All eyes will now be on United’s squad sheet which will be released an hour before kick-off at 4.30pm.
If Ronaldo and Cavani are both missed for the match against Pep Guardiola’s champions, United will face a selection dilemma.
Marcus Rashford, who has played as a winger this season, may have to line up as a striker.
This would likely see Anthony Elanga join Jadon Sancho on the flanks, leaving United running out of attacking options from the bench.
Eric Bailly is back in the team after an injury, but Victor Lindelof would be the man to replace Varane.
As for Shaw, United have two options in Alex Telles and Diogo Dalot.
Man Utd squad confirmed at Lowry Hotel: De Gea, Henderson, Heaton, Dalot, Wan-Bissaka, Jones, Maguire, Bailly, Lindelof, Telles, Matic, McTominay, Fred, Pogba, Mejbri, Lingard, Mata, Fernandes, Sancho, Elanga , Rachford.