Ponte di Legno - Italian cyclist Danilo Di Luca, currently competing at the 96th Giro d'Italia, has been "provisionally suspended" after testing positive for EPO in an out-of-competition test before the race.
Di Luca, who has already served a ban for failing a doping test at the Giro and has been embroiled in other doping affairs, tested positive for the banned blood booster at the end of April.
Cycling's world governing body, the UCI, said it had "provisionally suspended" the rider, who risks a heavy sanction if found guilty.
"The decision to provisionally suspend this rider was made in response to a report from the WADA accredited laboratory in Cologne indicating an Adverse Analytical Finding of EPO in a urine sample collected from him in an out of competition test on April 29, 2013," the UCI said.
"The provisional suspension of Mr Danilo Di Luca remains in force until a hearing panel convened by the Italian Cycling Federation determines whether he has committed an anti-doping rule violation under Article 21 of the UCI Anti-Doping Rules."
Di Luca was without a contract at the start of the season but managed to sign for the second division team Vini Fantini, who were assured a place in the three-week race.
Team boss Angelo Citracca indicated upon hearing the news the team would sack the rider if a 'B' sample confirms the first result.
"This result reflects upon the whole team," said Citracca.
Despite having only two days of racing in his legs, the 37-year-old Di Luca was called into the team in time for the May 4 start in Naples. Although he has failed to win a stage or challenge for overall honours, Di Luca has often been seen on the attack.
Di Luca finished 10th in Thursday's uphill time trial behind stage winner and overall race leader Vincenzo Nibali, who now has a 4:02 over his closest rival, Australian Cadel Evans, with two stages to race. The Italian sits in 26th place overall at just over 33min behind Nibali.
A former race winner, in 2007, Di Luca has a doping past. He returned two positive doping tests from samples taken during the 2009 edition of the race, which he finished as runner-up behind Russian Denis Menchov.
Di Luca denied doping at that time but finally confessed and earned a more lenient sanction. Instead of a two-year ban, he was suspended for 15 months.
Di Luca also returned abnormal results from test samples at the 2007 edition of the race, which he won.
It prompted a prosecutor to demand a two-year ban, but the cyclist was cleared at the 11th hour by the Italian Olympic Committee (CONI) due to a lack of evidence.
Disgraced American Lance Armstrong, who was stripped of his seven Tour de France crowns among other victories due to doping, reacted to the news via a message on his Twitter feed.
The American said: "Knowing I have 0 cred on the doping issue - I still can't help but think, 'really Di Luca? Are you that fucking stupid??'."
Friday's 19th stage, the first of two consecutive days in the mountains, was cancelled by organisers because of heavy snow and sub-zero temperatures on a revised route.
Changes were also made to Saturday's 20th stage, the last in the mountains, due to the conditions.