Sauber's Sergio Perez is to be kept in hospital for a second day after a heavy crash in Monaco Grand Prix qualifying.
Sauber chief executive officer Monisha Kaltenborn told BBC Sport: "He has concussion and a bruised thigh and will be kept in for at least another day."
She added that he was "in good spirits" but that it was "too early" to say whether he would be fit to race in the Canadian Grand Prix in two weeks' time.
The Mexican crashed exiting the tunnel and hit the barrier at the chicane.
Sauber said he had spent a "good night" in the Princess Grace Hospital and had had further medical examinations on Sunday morning.
Medical staff said he would stay under observation for another night before having a second brain scan on Monday.
Kaltenborn added: "Sergio is doing very well, he had a good night and is chatting away."
Perez, 21, who is in his first season in F1, had already been ruled out of Sunday's race.
BBC F1 pit-lane reporter Lee McKenzie said Perez had been keen to race but that doctors would not let him.
Sauber are to launch an investigation into the cause of the accident.
Perez was off line as he came out of the tunnel and was still in the middle of the track when he lost control as the circuit starts to go downhill towards the chicane.
He was at least a full car's length to the left of the racing line, and the lack of grip on the dusty surface there almost certainly contributed to his accident.
Perez hit the barriers side on and the session was stopped for half an hour while crews extricated him from the car and took him to the medical centre before the barrier was repaired.
Perez's accident was the third this weekend suffered by a driver coming out of the tunnel and heading to the chicane after Renault's Vitaly Petrov also crashed there on Thursday and Mercedes driver Nico Rosberg suffered a similar incident at the same place in final practice.
Rosberg's crash was caused by him locking his brakes over the bumps at that part of the track, to which low tyre pressures probably contributed, according to Mercedes.
Unlike Perez, he narrowly missed the barriers at the chicane, coming to a halt in the middle of the track after the corner.
Rosberg's car was launched into the air by 'sleeping policemen' in the run-off area at the chicane, but race director Charlie Whiting had these removed before qualifying to prevent that happening in any later crash.
Button, who crashed at the same place in 2005, said: "Sergio Perez had a big accident, I'm glad he is OK.
"I know how hard the barrier is there. The g-forces you pull are incredible."
Button praised Whiting's decision to ban the use of the DRS overtaking device - which works by reducing drag on the straights - in that part of the Monaco track.
"I'm really happy that we don't have DRS there; it was a great decision by the FIA," he said. "Even without it we see that this is a danger spot for us.
"Under braking it is a little bit bumpy and as soon as you lock the rears there you are a passenger and you're into the wall. You are just sliding along like a sled and it always aims for the middle barrier.
"Over the years we have improved the circuit since Karl Wendlinger's accident [for Sauber in 1994] - which was horrific. But still we could have a big accident.
"We all love coming here and this is a great place to race but I still think we can improve the safety in that area. This is a great circuit and it would be nice to improve it.
"After Nico's accident this morning he lifted as he went over those humps and we asked for them to get removed and Charlie removed them, which is great.
"If the car had hit them it might have jumped up in the air and hit them at a different angle."
Wendlinger was in a coma for 19 days after hitting the barriers side on at the chicane at a time when F1 cars had far less cockpit protection and the barriers were less advanced.
Championship leader Sebastian Vettel said he had been asking for updates on Perez's condition as he waited in his car for the session to be restarted.
He joined all the leading drivers in saying their thoughts were with him and offering hopes that he would be back in the car soon.
"There is a shadow over the last qualifying session with the accident Sergio Perez had," Vettel said.
"We were all waiting and I was asking if we can get an update. Hopefully he is racing soon. It is hard to retain your focus."