Ronaldo is looking for options to exit Manchester United this summer.
After only returning from Juventus, the 37-year-old wants to leave Old Trafford.
However, Ronaldo remains motivated by his desire to play in the Champions League this season.
The five-time Ballon d'Or winner hopes to maintain his position as the competition's leading scorer.
Ronaldo currently leads the league with 140 goals, 15 more than Lionel Messi.
Ronaldo, on the other hand, is three goals behind Messi in group-stage goals, which is a motivating factor.
According to reports, his agent, Jorge Mendes, has held talks with Sporting in order to find a way out of Old Trafford.