Belgian track rider Tim Mertens underwent exploratory heart surgery Wednesday and will miss the Gent Six Day, November 24 to 29.
Mertens, 23, did not feel well at the World Cup meet in Manchester earlier this month. He dropped out of last week's Munich Six Day race on the first day with reported circulation problems.
The surgery should clarify what the problem is and how serious it is.
Mertens also made his professional debut on the road this season, riding for the Belgian Professional Continental team Topsport-Vlaanderen.