Wimbledon faces a major matches backlog after showers caused much of Wednesday's play to be lost to the weather.
Only 18 of the billed 74 matches were completed, and Britain's Heather Watson will head into a second day of her delayed first-round match against Germany's Annika Beck on Thursday.
The Centre Court retractable roof meant some live tennis was possible throughout, and anxious organisers added two matches to the schedule on the main show court late in the day.
The roof has been in place since 2009, and was made for days such as this. Its use meant Agnieszka Radwanska, Novak Djokovic and Roger Federer got through their matches without getting wet, and the clashes involving Belinda Bencic and Eugenie Bouchard were also moved across to the 15,000-capacity arena in the evening.
An intended start at 11.30am on the outside courts had been immediately put back due to spots of rain, and action began almost an hour later than planned, before soon being stopped just before 1pm by a fresh arrival of showers in south-west London.
That brief window had been sufficient for Andrea Petkovic and Tomas Berdych to complete their first-round matches, which were among 30 that had been either unfinished or yet to start when a wet-weather interruption cut short play on Tuesday.
Come the end of the day, after intermittent showers caused play on all but Centre to finish by 6.30pm, the weather problem was mounting for organisers.
Wimbledon last saw play on the middle Sunday, traditionally a rest day, in 2004.
The 'People's Sunday' option is only considered in drastic circumstances, and the lost of a day and a half to the wet weather appeared unlikely to force the tournament's hand at this stage.
However, with showers forecast for Thursday, Friday and Saturday, the tournament may find it needs to forfeit its day off.
A host of second-round singles matches were called off for the day, including those involving Garbine Muguruza, Venus Williams, Madison Keys and Milos Raonic.
The day's doubles matches were also scratched from the programme. Wimbledon announced the first round of the men's doubles would be reduced from best-of-five-set to best-of-three contests, in an effort to help with the schedule.
Wimbledon is due to have a cover on Court One in time for the 2019 championships, which will allow play to also continue in that arena while rain falls outside.
Thursday's order of play was not too significantly different to previous days when it was announced, the main change being an 11am start on the outdoor courts.
Watson will kick things off on Court 12, with all the outstanding first-round matches slated to go first.