“I’m suspicious of the hidden agenda of politicians,” Macron told a news conference on Tuesday amid growing talk that Valls was about to make his intentions known.
Valls, who lost to radical leftwinger Benoit Hamon in the primaries, is seen as waiting in the wings to pick up the pieces of the Socialist party after the presidential race and build a reformist force in parliament to get a say in a Macron parliamentary majority.
The pro-business former premier has been scathing about his former education minister.
Hamon signed a motion of no-confidence against Valls’ government last year, when the ruling Socialists split over a controversial labour reform led by Valls.
On Wednesday, Hamon shot back.
“I’m not surprised,” he told France 2 television. “This sort of soap opera is meant to weaken me. I’m running my campaign by talking about the French’s daily life, not Valls’ life.”