Flintoff will lead the England side which heads to Australia to defend the Ashes for the first time since 1986, however his former Lancashire teammate had some daunting words for him ahead of the series.
"The choice of Flintoff as captain is good but I fear he will be leading a losing team in the forthcoming Ashes," Wasim told AFP.
"The Australians are going to crush England and only an extraordinary performance can avert the outcome."
Wasim, who skippered Pakistan in 25 Tests and 109 one-day matches is familiar with being a losing captain in Australia having lost 2-1 there in 1995 and 3-0 in 1999.
"I had two tours of Australia as captain and realised that they play very tough on their home grounds. I know their wickets and they are very hard for newcomers to adjust on," said Wasim.
"Flintoff is an inspirational cricketer and leads from the front which is a good quality for a captain, but only the upcoming Ashes will mature him," he added.
The swing bowling specialist also highlighted England's pre-Ashes injury list as another reason they could be put to the sword in Australia.
"They (England) are already without their key batsman Michael Vaughan and effective paceman Simon Jones and they might lose some other players through injury in the early part of the tour," said Wasim.
"For me Australia are huge favourites and they would be at their worst if they lose."
The first Ashes test begins on November 23 in Brisbane, followed by matches in Adelaide, Perth, Melbourne and Sydney.