Bayern Munich great Ze Roberto believes Cristiano Ronaldo will hang up his boots before the age of 40 following a drop in performance over the last few years. 

In his return to Old Trafford, 37-year-old Cristiano Ronaldo made an electrifying start, netting eight goals in his first 15 league appearances and playing a crucial role in guiding Manchester United to the Champions League knockout stages. Yet, as the new year dawned, his scoring touch has faltered, with just one goal in his last 10 matches across all competitions.

Cristiano Ronaldo, 37, is in the twilight years of his career and is currently in a slump of form+7View gallery

And Bayern Munich icon Ze Roberto (pictured) doesn't think Ronaldo will play past the age of 40+7View gallery

Bayern Munich icon Ze Roberto (right) doesn’t think Cristiano Ronaldo (left) will play past 40

His recent difficulties had brought his future into question, with many questioning whether the Portuguese talisman should now hang up his boots.

And Ze Roberto, who himself went on to play until the age of 43, believes the time to make that decision may come sooner than later after what has been a spectacular career thus far.

‘Cristiano is, for me, a machine,’ Ze Roberto said to 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.

Ronaldo's output has dramatically decreased since re-joining his old side from Juventus+7View gallery

Ronaldo’s output has dramatically decreased since re-joining his old side from Juventus

Ronaldo made a strong start but has suffered a drop in form and is struggling for goals+7

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Ronaldo made a strong start but has suffered a drop in form and is struggling for goals

‘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.’

While many have questioned Ronaldo’s future – including former Chelsea striker Frank Leboeuf – the 37-year-old is determined to add more silverware to his collection despite having won multiple trophies at United, Real Madrid and Juventus.

And Ze Roberto (right) believes Ronaldo will hang up his boots in a couple of years as a result+7View gallery

And Ze Roberto (right) believes Ronaldo will hang up his boots in a couple of years as a result

He even claimed that he would hang his boots up in ‘four to five years’ time, given that he is the model athlete and his meticulous approach to fitness, his lifestyle and diet has seen him stay at the top level for so long.

When asked about his future, Ronaldo said that he wanted to continue playing football in his 40s and insisted he had no plans to retire while the possibility of more trophies was still there.

Speaking to DAZN, Ronaldo said: ‘It’s hard to say that I don’t want more, because if I’m at a club that gives me the opportunity to win more things, why not?

‘And in the national team too. I know I don’t have many years left playing, four or five more, we’ll see, and I want to win more things.

However, Ronaldo himself revealed he wants to play at the top level for at least four more years+7View gallery

However, Ronaldo himself revealed he wants to play at the top level for at least four more years

‘You have to be intelligent and know that at 18, 20 or 25 you are not the same as at 35. And that is the maturity, the experience, the intelligence to understand that maybe you lose some things to win others and have the right balance to continue competing and be at the highest level.’

When asked about the criticism he has received, Ronaldo said: ‘I show year after year that the numbers speak for themselves. I don’t have to tell you that I’m very good, because the numbers are there.

‘The facts are facts, the rest is not It doesn’t matter at all. That’s why I’m very happy with my form, I’m still scoring goals, helping people, teams, both in the national team and at Manchester United and that’s why I want to continue like this.’

Ronaldo was also questioned on how he had managed to achieve sustained success over two decades – Ronaldo said it was all down to his ‘sacrifices’.

Ronaldo says the secret his success over the years have been the sacrifices he has made+7View gallery

Ronaldo says the secret his success over the years have been the sacrifices he has made

‘You have to sacrifice as without sacrifice you achieve nothing,’ Ronaldo stated. ‘I started playing at the top level at 18 and I’ve been at the top of the game for 15-16 years.

‘It’s my dedication, my passion, my ambition to be working hard all the time. This is why I continue to be at the top of the world in terms of performance, trophies, goals, records. I will continue.’

However, Ronaldo’s future at Manchester United is up in the air. He will wait and see who the new Red Devils manager is before deciding on his future.

As it stands, Ronaldo is contracted at the club for a further season. However, there is growing uncertainty over his future as the club are facing an uphill challenge to qualify for next season’s Champions League.