Fernando Alonso "knows best" when it comes to deciding whether to return to Formula 1 next year.

That is the view of future Ferrari driver Carlos Sainz's father and namesake, when asked by Italy's Sky Sport 24 to comment on speculation linking family friend Alonso with Renault for 2021.

On the face of it, returning from sabbatical with Renault is a risky move for 38-year-old Alonso, after Daniel Ricciardo made the decision to flee amid reports of big financial trouble at the parent company.

Reportedly, having secured a EUR 5 billion government-backed loan, Renault is now poised to close car factories and announce billions in savings.

Another rumour is that Liberty Media would help Renault to pay Alonso.

"Fernando has the right to decide to do what he wants," rally legend Carlos Sainz snr said.

"I would be happy to see him on the track again but he knows best of all what to do. As a friend and fan, I will respect what he decides."

However, Alonso's former Daytona teammate Renger van der Zande thinks the Spaniard should resist the lure of returning to Formula 1 with Renault.

"For the story, a comeback with Renault is of course very nice," he told Algemeen Dagblad newspaper. "But I don't see Renault becoming world champion next year.

"And if Alonso goes somewhere to drive, it should be with a team that can win.

"If he comes back, he will have an enormous drive to prove himself," van der Zande added. "But he left Formula 1 to try other things - Daytona, Indy, Dakar. And he will not have much choice if he returns now.

"Maybe he'll do it if he gets a really good offer, but I don't really expect it to happen," he said.

"I understand that people would like to see it happen, but just look at how Michael Schumacher fared. He was absolutely the best, but not when he returned.

"I think Alonso has more to lose than to win by coming back," added van der Zande.