Guimard won seven stages at the Tour de France as a rider and seven overall titles as a director of Bernard Hinault, Laurent Fignon, and Lucien Van Impe.
Speaking to Cyclism'Actu, he explained that he would not put Froome, Egan Bernal and Geraint Thomas - the past three Tour winners - in the same line-up, as Ineos are set to do next month.
As well as still being on the comeback trail from a career-threatening injury, Froome recently confirmed he will leave Team Ineos at the end of 2020 and move to Israel Start-Up Nation.
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"He'll be there, without doubt, but how will it play out? Honestly, I wouldn't put the three of them on the start line," Guimard said.
"In any case, Froome will be like gunpowder. At what moment will the spark light the fuse that blows everything up. It's impossible to know, but who sees Bernal telling Froome to ride for him from the bottom of a climb until he's empty? Unless Froome is strong, but if he's not, why pick him and leave out another good domestique? That could lead to a clash, because either Froome is not going well and it's not worth putting him in the team, or he's going well and then Ineos have a sword of Damocles hanging over them every day.
"It could be an extraordinary chance to see Ineos explode during the Tour. The three of them on the start line, that opens doors for their rivals. It would be good for [Thibaut] Pinot, [Romain] Bardet, [Nairo] Quintana, and Jumbo-Visma. It'll be interesting, there's going to be a race."
Regarding Froome's transfer to Israel Start-Up Nation, Guimard felt there was no other choice for the four-time Tour champion given the emergence of Bernal, who became the youngest Tour winner in more than 100 years last year at 22.
"Froome had to go - that's obvious. When you have a rider who has won four Tours, and another who has won one and has the potential to win four or five, it's not possible to have them in the same team. Except if Froome had said 'I can't win another Tour, I'll put myself in service of the young guy', but that's not in Froome's nature," Guimard said.
"At a certain level, when you're in a team it's not to hand out gifts, it's not to help a teammate win a race like the Tour. He could do it at Paris-Nice, but not the Tour. So for all that he couldn't stay at that team, and Ineos couldn't keep Froome and turn their backs on Bernal. Bernal had been very clear: he's the boss, full stop. From there, Froome's departure was inevitable."