World drivers' champion Michael Schumacher was close to retiring from Formula One following the attacks on New York and Washington.
The concerns of the German who drives for Ferrari were revealed by the Italian team's technical director Ross Brawn on BBC radio on Sunday.
Speaking a few hours before the United States Grand Prix in Indianapolis, Brawn said Schumacher had been deeply affected at the Italian Grand Prix which took place in Monza only a few days after the attacks.
"When he arrived in Indianapolis he was still feeling the effects of Monza," said Brawn.
"He really was badly affected by the disaster. There was talk of retirement. I think a few days of consideration reminded him how much he loves racing."
Schumacher, who has already secured the title this season, starts on pole position in Indianapolis where he is seeking his ninth victory of the campaign.