The ATP is to review the scheduling of matches after Andy Murray's meeting with Philipp Kohlschreiber in the Madrid Open began at 01:12 local time.
Several lengthy matches on Wednesday night forced the late start of Murray's second-round victory.
Murray's 6-4 3-6 6-0 win finished at 03:00, and he is due to face Spain's Marcel Granollers on Thursday evening.
"The scheduling issues in Madrid were unfortunate," said ATP Tour chief executive Chris Kermode.
Murray's match was delayed after Roger Federer's three-set defeat to Nick Kyrgios took two hours and 37 minutes, while Granollers needed three hours and 20 minutes to beat Gael Monfils.