McLaren's Eric Boullier believes a full WEC programme in 2018 would represent a "distraction" for Fernando Alonso and his commitment to F1.
The Spaniard will likely join Toyota next year for an onslaught on Le Mans, but it has also been suggested that Alonso could run in the majority of the World Endurance Championship events with the Japanese manufacturer as they do not clash with F1.
Boullier doesn't appear too keen on that prospect however, believing the undertaking would be physically demanding and distract the driver from his primary F1 duties.
"I don't think you can physically do two programmes, it is too complicated," said McLaren's race director.
"If you commit to two programmes it is a huge distraction. Doing Le Mans, or doing Indianapolis, or doing Daytona, why not? Because it is a one- off.
"But doing more than this would definitely be a distraction from his main commitment which is F1."
Alonso extended his contract with the Woking-based outfit for 2018, a year which will hopefully see a resurgence at McLaren following its decision to ditch Honda and partner with Renault in the future.
A provision in the Spanish driver's contract however allows for Alonso to venture beyond F1 as he attempts to fulfill his ambition of winning motorsport's Triple Crown, with victories at Monaco, Le Mans and Indianapolis.
"He said he is keen to do some races outside this triple crown, and there are case-by-case discussions," said Boullier.
"Obviously his main and his first focus is F1 – and that has priority. We will do everything we can to give him a competitive car and if we do this he will not race anything else."