Organisers said that play would not resume before 10.15pm local time (21:15 BST), on a day in which both last four clashes in the men's tournament were affected by bad weather.
Casper Ruud's 6-1, 6-1 demolition of Luciano Darderi was paused for nearly two hours earlier on Friday after a thunderstorm rolled over the Italian capital.
Sinner is hunting a record-breaking sixth straight Masters 1000 tournament victory ahead of the French Open which starts later this month.