Andy Farrell says the British and Irish Lions will assess Tomos Williams' hamstring injury after he limped off the pitch during his side's 54-7 victory over Western Force.
The Gloucester scrum-half produced a fine display on what was his first start in a Lions jersey.
He gathered from Henry Pollock to tap down his first try in the 16th minute.
Williams then rounded off a sublime Lions counter attack, leaping over in the corner following a slick one-two with James Lowe.
But having notched his second try of the contest, Williams was left clutching his left hamstring, briefly receiving treatment before swiftly being replaced by Alex Mitchell.
It was a cruel end to what had been a very promising performance from the Welshman, with former England and Lions back Ugo Monye hailing Williams' performance as "exceptional" while on commentary duty for BBC Radio 5 Live.
And head coach Andy Farrell confirmed Williams will be assessed on Sunday.
"It's a tight hamstring," said Farrell, speaking to Sky Sports in his post-match interview.
"You don't know what these things are like. Hopefully it's a bit of cramp, but we'll assess that certainly in the morning."
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Speaking as part of Sky Sports' commentary team, three-time Lions tourist Will Greenwood was quick to show his concern for the Wales international.
"I'm just hoping Tom Williams is ok," he said.
"Rob Howley, 1997, right in amongst it, he did his shoulder against the Sharks.
"And a hamstring, fingers crossed for him."
Williams' latest efforts followed what was an encouraging showing off the bench in the 24-28 defeat to Argentina in Dublin in the tour's opening fixture eight days earlier.
But he now faces a race to be fit for the first Test against Australia - which takes place at Brisbane's Suncorp Stadium on July 19.
Farrell's troops return to action against Queensland Reds on Wednesday.
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