Stuart in 2002 led the Roosters to their first National Rugby League premiership in 27 years, but he was axed on Monday after two disappointing years for the club.
Gregan is confident Stuart, who was a prodigious union talent in his schoolboy days, could have a positive influence in a coaching role in the 15-man game.
"He's got a pedigree in rugby," Gregan told ABC Sport.
"Who knows, I guess you should be asking Ricky, but he is a very astute coach and he has a very good understanding of both codes.
"He's passionate about league but he knows a thing or two about rugby union. I guess if the opportunity was there, I am sure we'd have a look at it."
Meanwhile, as the Wallabies seek to record their first win in South Africa since 2000 in the clash with the Springboks at Ellis Park on September 9, Gregan insists his side will be ignoring the fact that the Springboks are yet to win a Tri Nations match this year.
"There'll definitely be some doubt, but they will be very, very pumped up," he said of South Africa, who lost to the All Blacks in Pretoria last weekend.
"They are always a very, very good team, very formidable at home and I think you saw it during some different periods of that game in Pretoria against the All Blacks.
"They were very competitive but it is going to be something that we are very prepared for and the guys are keen for the challenge."
The Wallabies fly out to South Africa on Friday.