Portuguese cyclist Andre Cardoso has been suspended by his team for a failed drugs test, four days before the start of the Tour de France.
The 32-year-old, one of nine men in the Trek-Segafredo team that includes 2009 Tour winner Alberto Contador, tested positive for erythropoietin (EPO).
Cardoso's sample was taken at an out-of-competition test on 18 June, said the International Cycling Union (UCI).
Spanish rider Haimar Zubeldia will take Cardoso's place in the team.
EPO boosts the production of red blood cells, which speeds up the delivery of oxygen to muscles.
A Trek-Segafredo statement read: "It is with deep disappointment that we have just learned that our rider, Andre Cardoso, has tested positive for a prohibited substance.
"In accordance with our zero-tolerance policy, he has been suspended immediately.
"We hold our riders and staff to the highest ethical standards and will act and communicate accordingly as more details become available."
Cardoso has completed seven Grand Tours but never raced in the Tour de France, which runs from 1-23 July.