The Portugal international has reportedly asked to leave Old Trafford for a club who are playing in the Champions League.
United cannot offer him football at that level after the team only finished sixth in last season's Premier League.
Ronaldo finished as top scorer in his first season back at United with 24 goals in all competitions, but he was absent from pre-season trips to Thailand and Australia and only returned to action in Monday's (AEST) 1-1 friendly draw with Rayo Vallecano.
Cristiano “The King is back Sunday” Ronaldo didn’t even wait for the final whistle to leave the stadium 😭😭😭 pic.twitter.com/EWKRYXU0MI— Madrid Fan (@cristiano_peak) July 31, 2022
Even that was not without controversy as Ronaldo, who started the game but made way for Amad Diallo at half-time, was pictured leaving Old Trafford while the second half was ongoing.
Saha played with Ronaldo during the 37-year-old's first spell at the club, and believes his former colleague needs to look at the wider picture.
"In some way, from Cristiano Ronaldo's point of view it's a bit unrealistic to ask now a club of this size to adapt to him and his dream," Saha told Sky Bet in quotes reported by several British newspapers.
"I'm not Cristiano but as someone who seems to be a supporter of Manchester United, I have felt like he hasn't shown completely enough of that, he is thinking about himself.
"I am not going to judge him because he is an immense player and I'm not in his position, but I would have loved him to stay because he's a terrific player.
"No one can judge his actions at this moment because it's his own career."
Despite Ronaldo's reported desire to leave, a number of European giants have distanced themselves from signing him, with clubs such as Chelsea and Bayern Munich seemingly not interested in signing the 37-year-old.
It remains to be seen whether he will still be a United player when they open their Premier League campaign against Brighton and Hove Albion on Sunday, as they attempt to bounce back from a season where they achieved their lowest ever Premier League points total of 58.