When the same sources who announced Ronaldo was leaving Juventus before it was public claim he was in talks with City, yeah, it seems pretty credible to me. Especially when we had different sources in France who also announced Mendes was offering Ronaldo all over europe.
If you want another proof, just take Rio describing the calls he had with Ronaldo :
“I rang him (Ronaldo) straight away: ‘What's going on? Tell me you're lying.’ Every type of no, no, no in the conversation.
“I'm like all the fans, I'm exactly the same and we are all the same like that: ‘Please tell me you're not going?’
"Yesterday I think I probably spoke to Cristiano more than I've spoken to him since he left
#mufc, on text, on phone calls through the evening into the night. My missus just rolled over and said 'i'm going to bed, I can't deal with this".
"Sir Alex Ferguson would've been the exact same. He would've hated to see Cristiano in a Man City shirt, just like any other person that's been connected for a long period of time at this football club. "
I mean come on, why do you think Rio would spend the night talking to Ronaldo if he wasn't trying to talk him out of joining City.
Looks pretty compelling to me.