Sauber Formula 1 driver Pascal Wehrlein has been withdrawn from the Australian Grand Prix, with Ferrari's Antonio Giovinazzi set to make his F1 debut in his place.
Wehrlein injured his back in a crash at the Race of Champions in January and was forced to miss the first pre-season test at Barcelona as a result.
Although he completed the second test and was able to drive in Friday practice in Melbourne, he told the team on Saturday morning that he was concerned about his ability to finish the race so wanted to stand down.
Wehrlein said: "My fitness level is not as it should be for a full race distance because of my training deficit. I explained the situation to the team yesterday evening.
"Therefore, the Sauber F1 Team has decided not to take any risks.
"It is a pity, but the best decision for the team."
Ferrari third driver Giovinazzi stood in for Wehrlein in the first test at Barcelona and the 2016 GP2 runner-up will make his grand prix debut at the wheel of the C36 on Sunday.
Sauber is allowed to substitute Giovinazzi in for the season-opening grand prix under article 26.1a of the sporting regulations.
This stipulates that, subject to the consent of the stewards, teams are allowed to replace an entered driver as long as it is done before the start of qualifying.
Sauber does not have an official reserve driver at the moment, with Ferrari junior Charles Leclerc linked to the role earlier this month.
Team principal Monisha Kaltenborn said she was confident that Wehrlein would be fully fit in time for the Chinese Grand Prix.
"We have great respect of Pascal's openness and professionalism," she said. "This decision was definitely not an easy one for him, it underlines his qualities as a team player.
"The focus is now on his fitness level, and in such a situation we do not take any unnecessary risks.
"Pascal will be in China as planned."