Duenas Nevado was sitting in 19th place overall after stage 10
Team sponsor Barloworld will end its association with cycling following the positive doping test of one of their riders during the Tour de France.
Moises Duenas Nevado, who has been excluded from the Tour, tested positive for blood-booster EPO after stage four.
The team said the Spaniard's positive test had a "negative impact on Barloworld and our brand principles".
Barloworld's contract was set to expire in 2009 and discussions are under way for a replacement sponsor.
Chris Fisher, head of corporate marketing at Barloworld, said: "Team Barloworld has a zero tolerance policy towards doping, which has been constantly communicated to the riders.
"We have to act on this policy and, as such, we will all have to live with the long-term consequences of one individual's action."
Duenas Nevado's sacking and the retirements of Baden Cooke, Felix Cardenas, Paolo Longo Borghini and Mauricio Soler from the Tour has reduced the team to four riders.
Barloworld's announcement comes after Spanish team Saunier Duval withdrew from the Tour and sacked Italians Riccardo Ricco and Leonardo Piepoli for "doping practices".
Duenas Nevado was the second Spanish rider to test positive for the drug during the Tour after veteran Liquigas rider Manuel Beltran was sent home following a positive test after the first stage.