Ronaldo scored twice on his second debut for the club last weekend and also netted in their Champions League opener at Swiss side Young Boys.
The Portuguese is also an influential figure off the pitch - Red Devils teammate Lee Grant shedding fascinating insight into how Ronaldo is getting the players to watch what they eat without saying anything.
"This was Friday night in the group hotel," Grant told talkSPORT last weekend.
"So, as you guys will be aware, you finish your dinner and usually on a Friday night you've got a few cheat stuff out. You've got some apple crumble or you've got a bit of brownie and cream or what not.
"I tell you now, not one player touched the apple crumble and custard, not one player went up for that brownie because everybody was sat down and one of the lads said to me, 'What has Cristiano got on his plate?'
"So we were having a little goosey gander at what he has got and obviously it is the cleanest, most healthy plate you can imagine. And it just cracked me up how not one single player dared get up and have that junk food that was laid out."
Ronaldo's return reminds Danny Mills of Roy Keane, the talkSPORT pundit saying the 36-year-old back at Old Trafford would be like having the Irishman in the dressing room again.
"His influence off the pitch, around the training ground, not just the 90 minutes that he plays will be extreme," Mills said during Man United's clash at Young Boys on talkSPORT 2.
"Different personalities - but it's like Roy Keane stepping back into that dressing room and going 'if you want to win things, if you want to win the sort of trophies I've won and be as successful as me, this is what I do.'
"He won't say this out loud but he's one of the best players in the world, arguably the best, but his methodology, his training regime, the way he looks after himself, the standards he sets himself across looking after his body is second to none.
"There's no reason why everybody else can't be doing that and he will expect those sorts of standards."
Young Boys equalised in the 66th minute, prompting Ole Gunnar Solskjaer to make changes, including hooking Ronaldo off for Jesse Lingard on 71 minutes.
And Ronaldo could only look on in horror as Lingard's dreadful backpass went straight to Theoson Siebatchu, who bundled home the winner for Young Boys in the final minute of stoppage-time.
Download talkSPORT Edge NOW!
Whether it's goals as they go in or the latest from your club, stay up to date with everything going on in football with breaking news, live scores and in-app betting.
Download talkSPORT Edge in the App Store here.