Juan Martin del Potro could be in doubt for Wimbledon after withdrawing from the Queen's Club grass-court event because of a right knee injury on Wednesday.
The 12th-ranked Del Potro beat Denis Shapovalov 7-5, 6-4 in the first round but finished the match with pain and swelling in his right knee after slipping near the net in the eighth game of the second set.
The Argentine player underwent tests after the match, with organizers later confirming his withdrawal.
Wimbledon starts on July 1.
Milos Raonic, the sixth seed, returned from a back injury to fire down 24 aces in a 6-3, 6-2 win over Marco Cecchinato.
Rain washed out the entire day's play on Tuesday and more showers Wednesday have prevented two first-round singles matches — Feliz Auger-Aliassime vs. Grigor Dimitrov and Nick Kyrgios vs. Roberto Carbales Baena — from starting yet.