Manchester United forward Cristiano Ronaldo will have the hunger to score goals long after calling time on his playing career, says Manchester City boss Pep Guardiola.

The Portugal international has picked up from where he left off since returning for his second spell at United in August, scoring nine goals in 11 appearances.

That includes a dramatic double last time out against Atalanta in the Champions League to make it five goals in four games in the competition, three of those after the 81st minute.

Ronaldo is two goals shy of 800 goals in all competitions for club and country, a milestone he could reach in Saturday's crunch Premier League showdown with City.

Former Sporting CP, Real Madrid and Juventus man Ronaldo has scored three goals in his last five Manchester derbies, the most recent of those coming in May 2009.

Guardiola hailed the 36-year-old's longevity on the eve of the match as City look to end a run of four league games without a win against their fierce rivals.

"He will score goals all his life," Guardiola told Sky Sports. "He will be 75 years old, maybe retired, but he would be at his own barbecue playing a game and he'll score goals.

"Guys like [Lionel] Messi, like him, what they have done in the last decade in world football, scoring goals and goals and goals and helping their team win, speaks for itself."

Cristiano Ronaldo

Ronaldo finished as top scorer in Serie A last season with 29 goals, making him the first player to top the scoring charts in Italy, Spain and England.

That proved to be the five-time Ballon d'Or winner's third and final season with the Bianconeri before rejoining United in a shock transfer at the end of August.

City had been strongly linked with Ronaldo in the days prior to his United return being made official, but Guardiola was unwilling to confirm if his side were indeed in for the forward.

"You have to ask [United]," Guardiola said. "Ole [Gunnar Solskjaer] said that he could not imagine him to be here. You have to ask them.

"Do you think both are happy to have each other there? That's what's most important. It's good for the Premier League that he's back. United belongs to Cristiano and Cristiano belongs to United. It's a good fit.

"All that was in the past. Maybe it will be in the present and the future. We'll see."

Ronaldo is expected to start the derby between United and City at Old Trafford, but the Portuguese does not only have positive memories of this fixture.

He is the only player to have been sent off more than once in Premier League meetings between the neighbours, seeing red in January 2006 and in November 2008.