PARIS — Not so much the French Open as the French closed.

For the first time in 16 years, unrelenting rain Monday washed out a full day of play at the only Grand Slam tennis venue without a retractable roof over its show court, clogging the schedule with unfinished and postponed matches and prompting the frustrated tournament director to plead — again — for a roof as soon as possible.

"Our roof is a necessity," Guy Forget said, as players were sent back to their hotels and thousands of would-be spectators told to apply for refunds for their unused tickets.

"I'm a bit annoyed today, to say the least."

Chopped and changed plans to modernize Roland Garros now call for a retractable roof by 2020 over Court Philippe Chatrier, as part of a modernization of the cramped clay-court venue in the west of Paris. But opposition and legal action from local residents and environmental activists has slowed the ambitious project, which would expand Roland Garros into botanical gardens next door. Tournament organizers hope a ruling expected in September from the Council of State, France's highest administrative authority, will allow work to proceed.

With damp spectators sheltering where they could from the downpours and no letup forecast, tournament organizers announced in the early afternoon that there would be no play at all for the first time since May 30, 2000.

"We knew today was going to be horrible and it went beyond what we had imagined. That's why we sent back the players so early," Forget said.

If the weather breaks Tuesday, matches will start three hours earlier than initially planned and be spread over more courts. Despite forecasts of more rain, Forget said he is "pretty positive" there will be play. The schedule for Tuesday now has top-ranked Novak Djokovic against 14th-seeded Roberto Bautista Agut in the first match on Chatrier, playing for a place in the quarterfinals.

They will be followed by defending champion Serena Williams in her delayed fourth-round match against 18th-seeded Elina Svitolina. Venus Williams' match against 2015 semifinalist Timea Bacsinszky was supposed to have been played on Chatrier on Monday but was rescheduled as the third match Tuesday on Court Suzanne Lenglen.

The first men's quarterfinals are also scheduled: Second-seeded Andy Murray against Richard Gasquet is the third match on Chatrier, and defending champion Stan Wawrinka against Albert Ramos-Vinolas of Spain is scheduled last on Lenglen.

For the tournament to have the singles finals over the weekend as planned, players could be asked to play on consecutive days, as opposed to every two days, which is usual when conditions are ideal. That should not be a huge problem in women's singles, which play best-of-three sets, but could be tougher on men if their singles matches go to five sets. Forget didn't rule out that the finals could also be postponed.

"We are not that far back on schedule," Forget said. "If they do have, eventually at one point, to play two matches, then I guess the fittest guy will be rewarded for it."

The backlog also includes two fourth-round women's singles matches — Simona Halep vs. Samantha Stosur, and Tsvetana Pironkova vs. Agnieszka Radwanksa — that were pulled off court unfinished on Sunday evening because of rain and darkness.

Eight other fourth-round singles matches — four men's and four women's — also didn't get started Monday. Also postponed were more than 50 matches in the doubles and junior tournaments. There was no guarantee that Tuesday would be better: Weather forecasts for coming days were grim, with more downpours expected Tuesday before a hoped-for break in the clouds Wednesday.

With a new retractable roof scheduled to be available at this year's U.S. Open, the French Open is the only Grand Slam tournament without a structure for play to continue under rain.

"We have talked about that roof in Paris 15 years ago already. It is a long process," Forget said at a news conference as rain beat down outside. "For those in our country who are still doubting the necessity to expand, to modernize our stadium, I think we have right now the fact, the proof, that it is a necessity and we have to do it."