Four-time world 1,500 metre champion Hicham El Guerrouj may miss the Olympics unless a mystery breathing problem is cured.
The 29-year-old Moroccan suffered his first defeat since coming second in the 2000 Olympics when Bahrain's Rashid Ramzi beat him in Rome last Friday.
Double Olympic silver medallist El Guerrouj, the 1,500 metre world record holder, said he would decide whether to compete in Athens after the Zurich Golden League meeting on August 6th.
"I'm very worried about going to the Olympics or not," El Guerrouj told reporters ahead of the Lausanne Super Prix where he will attempt to return to winning form this evening.
"I'll make my final decision on August 6th in Zurich. I've been dominating for nine years but if I don't have a good world ranking position at the time I might not go to Athens."
El Guerrouj is taking daily medication to cure the breathing problem and is struggling to keep to his full training programme.
Before his defeat by Ramzi in Rome, El Guerrouj had recorded a 29-race unbeaten run.