Mo Farah has decided to run the 5,000m rather than the 10,000m at this weekend's Diamond League meeting in Eugene, USA.
The double Olympic champions has been struggling with a stomach virus and the problem is believed to be behind the decision to switch to the shorter distance.
Farah was set to face world record holder Kenenisa Bekele in the 10,000m but his main rival is now expected to be training partner Galen Rupp, who won a silver medal in London.
Fellow Brits Greg Rutherford, Robbie Grabarz and Christine Ohuruogu will also compete at the meeting.
