Juan Martin del Potro has suffered another stumble in his bid to regain full strength. The third-seeded Argentine has withdrawn from the Fever-Tree Championships with a right knee injury.

Del Potro slipped near the net in the eighth game of the second set of his match with Denis Shapovalov. Although the Argentine hung on for a first-round win, he underwent medical exams after noticing pain and swelling in his right knee.

“It is a great shame that Juan Martin has been forced to withdraw," said tournament director Stephen Farrow. "The crowd loves him here, just as they do all over the world. We wish him a full and speedy recovery, and hope to see him back here next year.”

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His second-round opponent, Feliciano Lopez, received a walkover into the quarter-finals. Del Potro also withdrew from the doubles draw with his partner, Horacio Zeballos. They will be replaced by Robert Lindstedt and Artem Sitak.

Del Potro has been limited to five tournaments since fracturing his right kneecap last October at the Rolex Shanghai Masters. He returned in February at the Delray Beach Open by VITACOST.com, but reaggravated the injury and was sidelined for another three months. The Argentine still intends to compete next month at Wimbledon.

He proved too consistent for Shapovalov on an overcast Wednesday, as the tournament attempted to play catch-up following Tuesday’s washout.

Watched by a 9,216-strong Centre Court crowd, third seed Del Potro came through a potentially tricky first-round encounter 7-5, 6-4 in 76 minutes at The Queen’s Club.

One break of serve in each set — at 5-5 in the first and at 2-2 in the second — was enough for Del Potro, who fell a few times on the lush grass. Del Potro hit 11 aces in their third FedEx ATP Head2Head meeting.

Shapovalov, who is currently in third position in the ATP Race To Milan for a spot at the Next Gen ATP Finals in November, got off to a 13-7 start in the first three months of 2019, but the Canadian left-hander is now 2-8 since March.

Sixth seed and 2016 runner-up Milos Raonic hammered 24 aces to defeat Italian Marco Cecchinato 6-3, 6-2. Awaiting the Canadian in the second round is Slovenian qualifier Aljaz Bedene, who rallied from a set down to defeat #NextGenATP Aussie Alex de Minaur 3-6, 6-4, 6-4. 

Frenchman Lucas Pouille raced through the last five games of his first-round victory over #NextGenATP Brit Jay Clarke 7-6(4), 6-1. He'll take on fourth-seeded Russian Daniil Medvedev in the next round. Pouille leads their FedEx ATP Head2Head 4-0, including a win last week at the MercedesCup. 

Rain prevented two first-round singles matches from starting. Eighth seed Felix Auger-Aliassime and Grigor Dimitrov will play on Thursday, as will Nick Kyrgios and Roberto Carballes Baena.

A full day’s play was washed out on Tuesday for the first time since the opening day of the 2012 championships.