Team BikeExchange-Jayco announced Tuesday morning that Luke Durbridge has become the fourth rider to leave the Tour de France after testing positive for COVID-19.

Durbridge, an Australian, was one of 165 riders who tested negative for the virus in a UCI (International Cycling Union)-established rest day test for all riders after stage 9 in Chatel.

However, prior to the 10th stage to Morzine, his team announced Tuesday that Durbridge had tested positive after suffering mild symptoms.

"Unfortunately, Luke Durbridge tested positive for COVID-19 this morning.

"Durbridge has very mild symptoms and will not start stage 10 today.

Durbridge follows Geoffrey Bouchard (AG2R Citroen), Guillaume Martin (Cofidis) and Vegard Stake Rengen (UAE Team Emirates), who contracted the virus during the Tour.

The fact that all the rest day test results were negative was a surprise, given the string of positive tests leading up to the Tour and the number of people infected during the race, especially among team staff.

The UCI requires all riders to be tested on the two rest days during the Grand Tour, but the new regulations call for rapid antigen testing, and PCR testing is performed in the event of a positive test.

The UCI does not require additional testing, but "strongly recommends" that teams themselves perform antigen testing "daily, if possible, and at least every two to three days."

After the race, Guillaume Martin expressed doubt that this internal testing was done by some teams, suggesting that the minor symptoms he reported to the team doctor were not reported by other teams.

The riders could technically continue with the Tour de France even if their test results were positive, depending on their CT scores, which indicate viral load and infectivity. Bob Jungels tested positive two days before the Tour, but showed only faint traces of the virus.