Serena Williams’ Wimbledon comeback just hit its first real drama.

The 23-time Grand Slam singles champion returned to Centre Court buzz this week for her first singles match in nearly four years, but her emotional comeback now comes with a cloud over it. Williams suffered a right knee issue during Tuesday’s first-round Wimbledon loss to 20-year-old Maya Joint, putting her planned women’s doubles appearance with sister Venus Williams in question.

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Williams, 44, pushed Joint into a gritty three-set battle before falling 6-3, 6-7 (6), 6-3 in a match that lasted 2 hours, 22 minutes. For long stretches, Serena looked like a player determined to remind the tennis world that even after years away, her fight hasn’t gone anywhere.

But according to her agent, Jill Smoller, Williams “tweaked her right knee at the end of the first set,” which explains why she skipped the usual postmatch media session. Smoller said Williams was excused by Wimbledon and WTA medical officials and left the grounds without assistance.

Now the question is simple: will Serena be healthy enough to stand beside Venus again?

The Williams sisters are scheduled to open women’s doubles against Camila Osorio and Solana Sierra later this week. That match already carried major nostalgia. Serena and Venus have won six Wimbledon doubles titles together, with their most recent All England Club crown coming in 2016.

Serena wasn’t listed for practice Wednesday, while Venus was scheduled to train alone. That doesn’t guarantee a withdrawal, but it definitely cranks up the suspense.

The comeback itself has never been sold as some ruthless chase for another trophy. Serena has been clear that this chapter is more personal than historic. After her singles loss, she said, “It was really great to be back at Wimbledon,” adding that the atmosphere and walk onto the court were moments she wanted to soak in.

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Last month at Queen’s Club, Williams said she wasn’t chasing validation.

“I don’t need to win,” she said. “I don’t have anything to prove.”

That’s true. But Wimbledon with Serena Williams is never just ceremonial. Even injured, even uncertain, even four years removed from singles competition, she still turns a draw sheet into must-watch theater.

Now Wimbledon waits to see if Serena and Venus get one more doubles ride.