The McLaren driver made his debut in IndyCar's blue riband event in May, starring in qualifying and the race before retiring with an engine problem near the end.

In Formula 1, however, the Spaniard and his team have struggled all year, having scored just two points in the first 10 races of a season plagued by reliability issues with the Honda engine.

The two-time champion has seen the chequered flags just three times so far, with a ninth place in Baku his best result.

When asked whether the first half of his season contained any positive moments, Alonso said: "Yes, the Indy 500."

Pushed to find positives besides Indianapolis, he replied: "No. We expected to be much more competitive and we are not delivering what our expectations were.

"We are working very hard to improve the situation as soon as possible, but definitely tough," he said.

Alonso's current contract with McLaren expires at the end of the year and he is yet to decide if he will continue with the Woking team, as he says he wants to be in a position to win races in 2018.

With the options of securing a drive with a frontrunning team looking slim, Alonso said a future in IndyCar was possible.

However, he insists F1 remains his priority and says he is open to moving to "any team" to win his third title.

"It [IndyCar] is there, it's one possibility. I've always said I'm very open that may come in the future. My priority is still Formula 1 and winning the third championship, but I'm open to find the way in any team to achieve that.

"I'm open to see another series if that is not possible for next year, so let's see in one month or one month and a half.

"I want to win next year and to win we need some good changes here, many changes here. If those happen, there'll be a possibility that I stay and that's something that I will have to consider in September."