The code-hopping league star left the San Francisco 49ers in May in a bid to qualify for the Rio Olympics with the Fiji Rugby Sevens team.
Lynch, in Australia to promote the US College Football season opener in Sydney this weekend, said on Thursday that while he was in awe of Hayne's athletic prowess, there was too deep of a cultural chasm for him to cross.
"He's a good athlete," Lynch said.
"I just think the culture of the game out here didn't translate back in the states."
The recently-retired Seattle Seahawks running back is in Sydney with his old alma mater University of California ahead of the Golden Bears' first game of the season against the University of Hawaii Rainbow Warriors at ANZ Stadium.
— South Sydney (@SSFCRABBITOHS) August 25, 2016
The man known as "Beast Mode" made a surprise appearance at South Sydney training at Redfern Oval, leaving several members of the Rabbitohs squad starstruck.
Lynch's PR man Grant Vandanberg also manages Souths co-owner Russell Crowe and shocked club officials late on Wednesday by informing them Lynch would be doing a last-minute photo op.
Lynch took a handful of questions from journalists, however needed Rabbitohs big man Sam Burgess to translate because he couldn't understand the Australian media accents.
He said Hayne was responsible for lifting the profile of American football in the country and he owed him a debt of thanks.
"I'd tell him thank you if he was standing here right now," Lynch said of Hayne.
"Because as I've been roaming throughout the city, a lot of people have been saying `that's that American football playing guy'.
"And I think his awareness brought it out."