Fernando Alonso is stealing the headlines heading into the Indy 500, but he's far from the first man to cross over from F1. (2:28)

INDIANAPOLIS MOTOR SPEEDWAY -- Mario Andretti says Fernando Alonso should consider a full season in IndyCar next year because his chance of finding a winning Formula One car are so slim.

Alonso is missing the Monaco Grand Prix to make his his rookie appearance at the Indy 500 on Sunday, a drive borne out of Honda's disastrous start to the season and uncompetitive power unit. The Spaniard has endured a difficult time since leaving Ferrari to join McLaren in 2015, finishing no higher than sixth in that time.

With his contract set to expire at the end of 2017 Alonso's future is currently uncertain and he has made it clear a third world championship remains his top priority. He has said he will decide on his future after F1's summer break in August but his chances of landing at a top team appear to be limited.

Andretti, a former world champion and Indy 500 winner, thinks Alonso would have no such problem finding a top seat in IndyCar and would still have time to return to F1 if he competed Stateside in 2018.

When asked by ESPN what Alonso should do in 2018, Andretti told ESPN: "Let me say it this way. It's my opinion, but I think at the end of the season if McLaren doesn't provide, or look like they're going to have something for him to look forward to the following year, I think his relationship might continue [in IndyCar].

"I don't know the contract. But let's put it this way, if McLaren doesn't produce in Formula One, I don't see where else he would go [in F1]. He's not going to go anywhere else with the top three teams... if he doesn't go there, there's a seat for him here, and a premier seat too.

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"He's a racer. He could probably even come here for one year and win his share, because he'll absolutely have the opportunity to do that, and then go back to Formula One. He's still young - he could go back to Formula One and one of the top teams he wants to be with. That would be a scenario and fantastic for IndyCar, definitely."

Alonso has been impressive since his first private test day at the Indianapolis Motor Speedway and qualified fifth for his debut race. Indianapolis Motor Speedway chief Doug Boles believes the excitement and appreciation Alonso has shown for the event has already endeared him to U.S. fans.

Andretti thinks Alonso's positive demeanour shows how much he is relishing the prospect of going into a race he has a good chance of winning.

"Monaco would be a difficult one to give up for anyone -- I know that, I've been in the middle of that one. Everyone that's happened up to him now justifies him making this move. I've not been around a lot but I follow Formula One but I don't think he has smiled at the racetrack as much as he's smiled here for quite some time.

"That's good to see, he's relaxed, confident. You can't do any better for any race driver than give them something that's competitive. He's starting second row here -- that's not for luck, he earned that, and I think he was a candidate for pole. So it's that close. When you're in that position that's a feel-good but you realistically have a chance to score."

Interview conducted by Alex Pombo.