Ronaldo, Madrid's record goalscorer, only signed a new five-year-deal last November, but is reportedly seeking to leave the Spanish capital following accusations he defrauded Spanish tax authorities out of €14.7million – a claim he strenuously denies.
The 32-year-old is reported to view a return to United as his favoured option if he does depart the Santiago Bernabeu, with Ronaldo winning three Premier League titles, an FA Cup, two League Cups and the Champions League during a six-year stay at Old Trafford between 2003 and 2009.
Carrick was a team-mate of Ronaldo's during that spell, but the midfielder is keen to wait and see how the scenario pans out.
"I haven't really given it too much thought to be honest with you," Carrick told Sky Sports.
"Listen, you don't need me to say, everyone knows what type of a player he is and how good he is and what a career he's had.
"It's not for me to get involved in whether he comes to Manchester United, whether he leaves Madrid or not, that's not my business at this moment in time.
"Of course, I was lucky enough to play with him. It was just a joy to work so close to him and see how he plays.
"We will see how it pans out over the next few weeks and months."