Fernando Alonso may sit out the final test of the 2015 pre-season in the wake of his Barcelona crash.
The Spanish double world champion has already spent two nights in hospital recovering from concussion and the effects of sedation given to him after the accident on Sunday.
Alonso's manager Luis Garcia Abad says the results of every medical test since the crash have been clear, but suggested that he may need to stay in hospital for longer.
The final four-day test of the winter, also to be held in Barcelona, begins on Thursday.
The impact was quite hard. We have to be sure everything is fine, so I can't say if it is one, two or three days more.
Luis Garcia Abad on Alonso's hospital stay
Abad said: "He will remain here (at the hospital) for the time we need to be sure everything is right and he gets out of here and back to normal life.
"The impact was quite hard. We have to be sure everything is fine, so I can't say if it is one, two or three days more," he told reporters on Monday.
McLaren-Honda admitted that it could mean Alonso misses the test, which is scheduled to conclude on Sunday, just two weeks before Melbourne season opener.
"We intend to give him every opportunity to make a rapid and complete recovery," said the team in a statement, "and will evaluate in due course whether or not he will participate in the next Barcelona test."
Keen to get back on track
Manager Abad said Alonso is already keen to get back to work.
"Fernando is very good," he said, "very optimistic and we are struggling to hold him back."
Abad does not rule out Alonso being sufficiently recovered to test this week: "We'll see what the doctors say, but right now the important thing is not winning the Barcelona test in February, but being able to fight for the championship until the month of November."
He also rubbished the wilder speculation about the cause of the crash.
"There were no explosions or alien abductions or anything like that," Abad quipped. "Alonso was driving the car and reducing speed before the impact, which is something you cannot do if you are not fully aware."
Finger pointed at McLaren
But respected journalist Michael Schmidt said McLaren only had itself to blame for triggering the wild theories.
"The Fernando Alonso accident shows that F1 still needs lessons in public relations," he wrote in Auto Motor und Sport.
"McLaren's policy of silence allowed the speculation to run wild," he suggested. "It (the team) could have stopped the problems with open communication."