Ronaldo, who signed for Juventus this summer in a stunning £105m deal, arrived back in Turin after his extended post World Cup holiday.
He greeted his new team-mates including Gonzalo Higuain and Paulo Dybala, whose places he has put under threat.
Ronaldo was pictured with both strikers despite the speculation around their futures following his arrival.
Ronaldo was strapped up to machines and to check his conditioning before the new season.
And he was snapped wearing an oxygen mask while running on a treadmill and was hooked up to monitors.
Ronaldo’s arrival has put pressure on Higuain and he could be shipped out to make room with Chelsea and AC Milan keen on a deal.
Dybala has also been linked with a move away from Juve following Ronaldo’s arrival.
The transfer stunned the football world after he spent nine years at Real Madrid, winning the Champions League four times and La Liga twice.
“The nine years at Real Madrid were wonderful, but it’s a brand new step in my life, so I thank all the supporters with my heart,” Ronaldo said at his unveiling.
“But I have to focus on this next step. I’m looking forward to playing. I’m very motivated, concentrated and focused on that.”
“I’m going to try to show that I am a top player, as usual. I’m going to work hard in training … I am very ambitious and I like challenges.
“I don’t like to stay in my comfort zone. After the experiences in Manchester and in Madrid, I’d like to mark the history of Juventus.
“It’s a big club and usually players of my age go to Qatar or to China, with all due respect, so coming to such an important and outstanding club at this point in my career makes me very happy. That’s why I’m very grateful to Juventus for this opportunity.
“[Juventus] have won domestic cups and Serie A titles, and they were in the final of the Champions League, so I am so proud to be here, I am so proud that they were interested in me.
“I hope I can give the best response on the field during matches, that’s what I can do. I hope I can take them to an even higher level.”
The five-time Ballon d’Or winner is expected to make his debut against Chievo on August 19 in the first game of the Serie A season.
Ronaldo has been shortlisted for the Best FIFA Men’s Player 2018 award alongside Lionel Messi, Kylian Mbappe, Mohamed Salah and Harry Kane.