Former F1 engineer Joan Villadelprat has questioned the wisdom of McLaren's decision to split with engine partner Honda.
The first week of pre-season testing in Barcelona concluded with Toro Rosso and the Japanese manufacturer achieving more laps than any other team, a feat which points to Honda's indisputable progress over the winter.
The Spanish engineer therefore has his doubts over the soundness of McLaren's choice.
"I already had reservations last year and I still do," he told Marca.
"I thought it was a hasty change and that they would miss all the advantages. As a customer you always have limitations, especially it seems when you are with Renault.
"I think French pride will drive them to very much want to beat them (McLaren)," said Villadelprat, who worked for McLaren, Ferrari, Benetton and Prost.
"I think the McLaren is a very developed car aerodynamically, but as the year progresses, Renault will move ahead.
"They are not investing all of that money from Paris without their own ambitions."
Villadelprat said all McLaren and Fernando Alonso can realistically hope for, therefore, is fourth place behind F1's top three front-runners.
"I do not doubt that Fernando will do podiums, but further than that I think will be very difficult," he added.
In light of Toro Rosso-Honda's performance last week at the Circuit de Catalunya, the engineer believes the Faenza-based squad could cause a few surprises in 2018.
"I do not rule out that they will be together with Renault and McLaren. I know very well that they fit perfectly with Honda and they want the project to work, as does Red Bull.
"I'm sure they (Red Bull) will take that engine in 2019 and will help in every way to develop it. Honda's potential is enormous if someone helps them to channel it," Villadelprat added.