Fernando Alonso has admitted that he may not have a more powerful Honda engine to use in Montreal this weekend.
Some media reports claim that while the struggling Japanese marque had planned to make a clear step in Canada, that specification will in fact not be ready.
Alonso, who is returning to McLaren-Honda after a one-race F1 absence, is quoted as saying by Diario Sport newspaper: "I don't know if we'll have something new for the engine in Canada, but I hope so.
"I did read that today, but I often read something in one place and something else in another.
"Until we arrive in Canada we will not know. But every time we do put a new engine in we will start last, because we have already exceeded our limits.
"So I think we have to choose the races in which we do change very carefully."
After being competitive at the Indy 500, the Spaniard said that he is returning to F1 with a positive and yet realistic attitude.
"I return with the impression of improving soon but I know it will not be immediate. But we will improve and everyone is impatient for that," Alonso said.
He also admitted that he would like to do the fabled Le Mans 24 hours in the future, but is not sure when.
"It is for the future - I do not have an exact date," Spanish media reports quote the 35-year-old as saying.
"Since I was a kart driver as a child I was dreaming about F1, Le Mans and Indy."
McLaren remain pointless in 2017 going into this weekend's race.
