A former Brazil star, who retired at 43, does not believe Cristiano Ronaldo will be playing football by the time he turns 40.
The Manchester United star turned 37 in February and has not revealed when he plans to hang up his boots.
Ronaldo has slowed down in recent years, but has never lost his scoring touch as he remains the Red Devils' top scorer this season with 16 goals.
Ze Roberto does not believe the five-time Ballon d'Or will be playing at the highest level in three years time.
"Cristiano is, for me, a machine," Ze Roberto told Sky Sports.
"But I don't think he will still be going at 40 because he is a player who has always played at the highest level, always winning trophies and always trying to be the best player in the world.
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"But in the last two years, we have seen he has not been able to do that with Juventus and now with Manchester United.
"The best proof of that is that he hasn't been among the top two or three players for the big individual prizes.
"He is still a player who costs a lot, but as someone who is used to competing at such a high level, there will come a time when he decides it is better to stop rather than look for something that won't be the same."