"There's a whole lot of people in the Ontario Liberal party who think that it's all over," Sorbara said Tuesday night in an interview on TVO's The Agenda with Steve Paikin.
Sorbara said Wynne has not sought his advice but he would tell her that it is "extremely unlikely" that she will win the next election.
"You have to ask yourself premier, whether given that scenario, it's better to step down before the next election," Sorbara said. "The (polling) numbers do not lie and the ability to win the next election is in grave grave doubt."
On the same program, one of the current Liberal campaign co-chairs, Tim Murphy, defended Wynne.
"I talk to lots of Liberals and not one of them wants her to go. Not a single one," said Murphy. "She's our best asset."
Wynne has said repeatedly she intends to stay on as leader to fight the June 2018 election.
On Wednesday, Sorbara clarified that he believes it is possible that Wynne can pull out a victory.
"Kathleen is a very good campaigner," Sorbara said in a phone interview with CBC News. "She needs at least to ask the question if someone else can turn around the fortunes of the party."
Sorbara lobbied for Wynne to become leader
Sorbara was Liberal campaign co-chair when Dalton McGuinty resigned as premier in 2012, triggering the party leadership race that Wynne won.
In his memoir, "The Battlefield of Ontario Politics," Sorbara says he used his influence behind the scenes on the day of the leadership convention to help Wynne, including encouraging candidate Eric Hoskins to take his delegates to Wynne after the first ballot. He also told reporters that Wynne's speech was "the best leadership convention speech" he had ever heard.
Sorbara served on Wynne's transition team. but he soon stepped down as the party's campaign chair and fundraising chair and played no role in the Liberals' 2014 election win.