Australian Evans won his only Tour title with BMC Racing and he now works as an advisor and ambassador for the team, which includes Froome's rival and former star domestique Richie Porte.
Froome, who already counts four Tour titles, announced he will race the Giro d'Italia this May 4 before trying for the Giro/Tour double and a fifth Tour win.
"He will be the favourite but if he finally does the double, he may not be as strong in France as last year," Evans told Marca.
Evans mentioned that he is following Froome's salbutamol case which could could see his 2017 Vuelta a España title stripped and him potentially forced to scrap his 2018 Giro plan.
With Porte in team BMC Racing, Evans said that they "would take advantage of the opportunity" if Froome showed any weakness from the Giro.
"[Porte] had a great opportunity in 2017, but in the end he was unlucky with the crash. I think he has all the physical characteristics to win it. He is trained, but we have to work together to forget the problems and bad luck, and this time, yes, get on the podium."
Their eyes will be on Froome. Evans twice rode the Giro and Tour – in fifth and 24th in 2010 and third and 39th in 2013 – so he knows what Froome will be facing.
"It's a difficult combination," Evans continued. "This year it's true that the Tour will start a week later [July 7], but there's a big difference because it comes at a crucial moment of recovery and it's close, so it will be interesting to see how his body responds."
News leaked on December 13 that Froome failed an anti-doping test for high amounts of asthma drug salbutamol in the 2017 Vuelta a España.
He said, "I took the greatest care to ensure that I did not use more than the permissible dose. I will provide whatever information it requires."
Froome and Team Sky are trying to prove that no foul play was involved. The case could drag on for months, in which time Froome is free to race. He confirmed his aims are still the Giro and going for a record-equalling fifth Tour win.
If issued a six-month ban, for example, he would still have time to return for the Giro. However, any decision in the Froome case could be appealed by both him or the World Anti-Doping Agency (WADA).
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