Ferguson's Premier League champions were comprehensively outplayed in May by a rampant Barcelona, who had United chasing shadows for the majority of their 3-1 Champions League final victory at Wembley Stadium.
Guardiola said the dominance of his all-conquering Catalans should not detract from Ferguson's trophy-laden reign at United.
"I cannot be compared with Ferguson," Guardiola told reporters ahead of Barcelona's friendly against Hajduk Split in Croatia on Saturday.
"The fact Manchester United lost a Champions League match doesn't mean I am a better coach than he is.
"I still have a lot to do just to attempt to be compared to him. The kind of prestige he has isn't lost for losing a match in the Champions League," added the Spaniard.
"When a person is working for more than 25 years and winning and winning and winning so many times, if there is one person I think is number one it is Alex Ferguson."
The Scot has led United to three Champions League finals in four years, winning in 2008 having also triumphed in 1999.
United overhauled Liverpool as the most successful English club in May when they won their 19th league title -- Ferguson's 12th Premier League crown since joining the club in 1986.