Saha played with Ronaldo at United for four years and was Bale's team-mate at Tottenham for six months in 2012.
Having played alongside both, the Frenchman has backed Bale to reach the same level as Ronaldo, if he mimics the Portuguese forward's commitment at training.
"What I saw from Bale in six months was amazing, I could tell straight away he would be one of the best. His physique alone was unbelievable - it wasn't normal," Saha told the Daily Mail.
"As a striker, you couldn't keep up if he went on the counter-attack. If he ran up the pitch and crossed straight away, I didn't have time to get into the box – he was too fast.
"But if you asked me the best I ever played with, it would have to be Ronaldo. He's in a different league to everyone else for now. And the work he put into his game was crazy, you can't imagine.
"Sometimes I've seen other talented players think they can get by on ability and think they don't need to work as hard as others.
"But Cristiano worked tremendously hard. He'd go to the gym, he'd do stretches and other preventative work to limit injuries, all that kind of thing. And he's improved year after year.
"He is a fantastic example for Gareth and I'm sure he sees the level of work and commitment that Cristiano puts in."
In his first season with Real, Bale has scored 21 goals in all competitions from 43 appearances, while Ronaldo has hit the back of the net 50 times in the 2013/14 campaign from 46 matches.
Saha is convinced that playing alongside the likes of Ronaldo and Angel di Maria at Real will only help the Welsh winger.
"No disrespect to Spurs (Tottenham) but being surrounded by Ronaldo, Luka Modric, Angel di Maria, players with big talent and experience, it will improve him," the 35-year-old former forward said.
"And you could see the effect on Spurs after Bale left. It shows how good he is.
"I think he made the right choice. Real is the right club, he was a bit injured and affected by the transfer saga at the beginning but you can see how he's improved in the second part of the season."
Bale and Ronaldo are set to line-up together for Real in Saturday's UEFA Champions League final against local rivals Atletico Madrid.
