Manchester United legend Wayne Rooney said he believes his former boss Sir Alex Ferguson still has the edge over Manchester City's Pep Guardiola when it comes to ranking the managerial greats.

Guardiola led City to a fourth consecutive Premier League title this season, a feat never managed by Ferguson or any previous team in the history of England's top flight. That took the former Barcelona and Bayern Munich manager's total haul to six Premier League titles in his eight seasons at Man City.

But that still falls some way behind Ferguson's record of 13 championships during his 26 years in charge of Man United.

"I think of course there are going to be arguments as to who is better, but I think people tend to just look at what Sir Alex did at Manchester United, and what he did at Aberdeen was incredible," Rooney said in an interview with ESPN Brasil.

"And you'd ask the question, could Guardiola do that at a team like Aberdeen?

"There's questions, there's debate, I think Guardiola for his era is of course the best and he's changed the way football is played worldwide ... but yeah for me Sir Alex, what he achieved in the game is incredible."

Prior to joining United, Ferguson won three Scottish titles with Aberdeen, breaking up the longtime dominance of Glasgow rivals Celtic and Rangers. Famously, he also guided them to victory over giants Real Madrid in the final of the 1983 European Cup Winners' Cup.

Guardiola, however, has the 3-2 advantage over Ferguson in terms of Champions League titles, with his two at Barcelona adding to last season's triumph as part of the treble with City.

Rooney spent nine years playing under Ferguson and eventually finished his career as the club's record goal scorer. However, he has made it clear that he has plenty of respect for Guardiola and earlier this year even suggested he'd be willing to work as the Spaniard's assistant.

"If Pep Guardiola comes in and asks me to be his assistant, you'd walk there," Rooney told the Stick to Football podcast.

"You see what [Mikel] Arteta is doing now [at Arsenal] and I strongly believe a lot of that is from learning what Guardiola was doing, and so it depends on what the situation is.

"For me, the best manager is Pep and you look at how he adapts -- how they [City] are playing now is not the same as how they were playing four years ago."

Since then, Rooney has himself returned to management, having been appointed boss of English Championship side Plymouth Argyle ahead of next season.