Giro d'Italia organisers said Monday they were tightening Covid protocols after positive tests claimed a series of big-name riders including leader Remco Evenepoel.
Geraint Thomas, who took over the race lead, said on Monday that "it's not the best way of taking it".
"Tt's a huge disappointment for the race and it might sound weird, but even for myself," Thomas said of Evenepoel's withdrawal. "I was looking forward to a real juicy battle."
Evenepoel dropped out late on Sunday after narrowly winning a long time trial.
Colombian rider Rigoberto Uran also pulled out with Covid on Sunday, his team EF Education announced.
Italian star Filippo Ganna, an Ineos team-mate of Thomas and second-placed Tao Geoghegan Hart, withdrew on Saturday following a positive test.
Three Jumbo-Visma riders were also withdrawn on the eve of the Giro.
Race organisers announced stricter rules during Monday's rest day.
"In the light of the latest developments concerning positive tests results on some riders, the direction of the Giro d'Italia informs that wearing a facemask will be compulsory in all areas of contact with the riders," said a race statement.
The statement said those areas includes team buses and areas it supervises at the start and finish of each stage.
On Monday, Thomas told a press conference that he was in favour of stricter measures.
"We just need to be more aware of it," the Welshman said. "Just go back to what we used to do in 2020-21. We were in a bubble wearing masks so I guess as a team, we're going to go back to that sort of strategy."
He added that while he agreed with the measures announced by organisers, he feared the virus may already be doing its damage.
"It's a good decision but at the same time maybe it's too late," said Thomas. "Some people might have already come in contact with it. But at least they're doing something about it now. it's a huge shame that guys have to pull out of a race because of any sickness really, so hopefully we can all avoid it."
- 'Heavy heart' -
Evenepoel quit the race late on Sunday, just hours after edging Thomas by one second in a long time trial. The 23-year-old Belgian faded in the final kilometres, as he had the day before when he lost time to his main rivals on stage eight to Fossombrone.
"It is with a heavy heart that I have to announce that I will be leaving the Giro d'Italia after taking a routine test, which unfortunately was positive," the world champion tweeted in a team statement.
He was the favourite to add the Giro to his Vuelta a Espana victory.
"My experience here has been really special and I was looking forward to competing over the next two weeks," Evenepoel added.
The rider was due to travel home on Monday by car.
His team, Soudal Quick-Step, said that all their other riders and staff tested negative.
The outbreak of Covid closely followed the controversy over the way riders got off the mountain-top at the end of Friday's stage to the snow-capped peak of Gran Sasso where team buses could not reach the finish.
Most teams used the public cable car, squeezing in with members of the public. Some teams, including Soudal hired helicopters to carry their stars away, drawing condemnation from the sports governing body, the UCI, for breaching the "principle of fair play and equity" and for increasing the carbon footprint of the race.
Most Ineos riders took the cable car, although Ganna rode down in a team car.
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