Two-time world champion Fernando Alonso's Formula One comeback is in doubt after he was involved in a road cycling accident on Thursday.
Alonso, 39, is conscious following the accident in Switzerland, but Italian media reported he has suffered multiple fractures.
The Spanish driver is due to return to the F1 grid this season following a two-year absence.
Alonso's Alpine team issued a short statement late on Thursday, saying: "Alpine F1 team can confirm that Fernando Alonso has been involved in a road accident while cycling in Switzerland.
"Fernando is conscious and well in himself and is awaiting further medical examinations tomorrow morning."
Testing for the new F1 season begins in Bahrain in only four weeks ahead of the first race, also in the Gulf Kingdom, on March 28.
Ferrari's Spanish driver Carlos Sainz tweeted: "Cheer up @alo_oficial. Hopefully it's nothing and you recover as soon as possible!"
Alonso has competed in 311 grands prix, winning 32 of them. He won successive championships with Renault in 2005 and 2006 before quitting McLaren after one season following a turbulent campaign alongside the then-rookie Lewis Hamilton.
He briefly returned to Renault ahead of a four-year period at Ferrari where he came close to winning the title on two occasions.
After falling out with the Italian team, he went back to McLaren, but the switch proved desperately unsuccessful.
In 2018, Alonso quit the sport and set his sights on becoming only the second driver since Britain's Graham Hill to complete the so-called Triple Crown – winning the Monaco Grand Prix, Le Mans 24 Hours and Indy 500.
Although he won the famous sportscar endurance race in 2018 and 2019 he has not been able to crack the Indy 500, despite a remarkable effort on his first appearance back in 2017.
This season, he is due to drive alongside Esteban Ocon at Renault, rebranded as Alpine for 2021, following Daniel Ricciardo's switch to McLaren.
