The triple Olympic champion Usain Bolt's 200 metres season is in jeopardy because of a strained Achilles tendon.
Bolt has switched to the 100 metres from the 200 for Friday's Diamond League meeting in Lausanne to avoid further injury.
Bolt developed a tightness in his left Achilles tendon in late May after running a 300 metres in Ostrava.
He has not run since and only resumed speed work last week.
He has the year's fastest time for the 200, having run 19.56 seconds in Kingston in May.
Bolt says Friday's race, his second 100 metres of the season, will be a good test for the tendon.
A bigger challenge will come next week when he is scheduled to race compatriot and former 100 metres world record holder Asafa Powell in Paris on July the 16th.
Powell has this year's fastest time over 100 metres at 9.82 seconds.