McLaren boss Zak Brown has rubbished suggestions Fernando Alonso could miss this year's Singapore Grand Prix to contest IndyCar's championship finale at Sonoma.

In May Alonso missed the Monaco Grand Prix to contest the Indy 500 in a McLaren entry powered by Andretti Autosport and Honda. Alonso's attempt to win the iconic oval race ended with a Honda engine failure, prompting him to declare he would return to the event in future.

Alonso's decision to skip Monaco was motivated by Honda's failure to deliver a competitive and reliable engine for the third consecutive year, and doubts remain over where he will be driving in 2018. The Spaniard is using Formula One's summer break to dwell on the decision.

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This week rumours circulated in North America that Alonso is considering another one-off IndyCar appearance in a fifth car run by Andretti Autosport at California's Sonoma Raceway, a race which clashes with F1's famous street race under the lights of Marina Bay on September 17. Brown has dismissed those suggestions.

"It's completely crazy," he told Racer. "He would have to first make that request through us, which he has not, and that event conflicts with F1 in Singapore. It's fake news."

Alonso has made it clear his top priority next year is to stay in F1 and find a car capable of challenging for the third world championship which has eluded him for a decade. McLaren and Renault seem to be the most logical destinations, though the uncertainty over Sebastian Vettel's next move has prompted rumours of a return to Ferrari in 2018 or 2019.

Fernando Alonso's orange McLaren-Andretti was a popular, surprise entry in this year's Indy 500 Jared C. Tilton/Getty Images

The questions over Alonso's future come with McLaren still weighing up whether to continue with Honda into 2018, though it appears too late for the team to switch manufacturers at this stage. Andretti Autosport is also in discussions which Chevrolet about an engine supply in 2018, which Racer suggests could thwart plans for McLaren to link up with the team for another Indy 500 appearance in future -- something both Brown and Michael Andretti have indicated a desire to do.

Brown says it is currently unclear how Andretti's engine plans would impact its hopes for another crack at the Borg-Warner Trophy, though he suggests a lot will hinge on its own relationship with Honda come next year.

"50-50; it could make a difference or not make a difference. It really depends where our Honda relationship goes as to whether it's important there would be a Honda engine in the car [at the Indy 500]."