The chances for Mardy Fish to play in his first ATP season final may have been badly compromised as the American suffered a hamstring injury in his first round match at the Swiss Indoors.
Fish was leading compatriot James Blake 1-0 in the opening set when he was forced to retire.
The retirement, after just 11 minutes on court, could mean the end of Fish's hopes of winning a place in the World Tour Finals in London later this month.
The 29-year-old stands provisional eighth in the race for the eight-man field, with three places still open.
The definitive line-up will be determined this week and next as the ATP winds up the regular season.
Fish, the No.1 American after replacing Andy Roddick, had been on a tear, winning 20 of 26 matches since July.
He still has 500 points of breathing space in the race between himself and provisional ninth-placed Spaniard Nicolas Almagro.
Blake will next play Russian Mikhail Kukushkin, who got into the field after Austrian Jurgen Melzer pulled out with a back injury.