Two-time Champions League, three-time La Liga, three-time Bundesliga and Premier League-winning manager Pep Guardiola "has a lot to prove", according to Eamon Dunphy.
The former Barcelona and Bayern Munich boss has just led Manchester City to the English title, wrapping up the Premier League with five games to play.
The Citizens could still become the first team of the Premier League era to reach the 100-point mark.
However, that hasn’t impressed the former Millwall man who maintains that Guardiola, who won a record four successive manager of the month awards from September to December, is still well behind the likes of Alex Ferguson, who brought Manchester United to the European pinnacle in 1999 and 2008.
"He has to change his philosophy," Dunphy told listeners on RTÉ 2fm’s Game On about the Catalan coach, who has won 23 trophies in 10 years.
"He has to sign some top-class defenders. He has a lot to prove, he really has.
"He is a good coach but he has a long, long way to go to get to where Ferguson was."
Dunphy feels that the 47-year-old must once again lead a team to the Champions League to be considered among the greats.
"Guardiola was hired to win the Champions League like he was at Bayern Munich.
"He didn't do it there and he is a long, long way from getting a Champions League victory with this team.
"He hasn't won the Champions League since 2011. We will see what he does at Manchester City.
"I'll make a prediction: he'll never win the Champions League again. And if he does, I will resign my position."