Scotland head coach Steve Clarke is "100% worried" about Billy Gilmour after the Napoli midfielder came off injured during the 4-1 friendly win over Curacao.

The 24-year-old will have a scan later on Saturday and Clarke says he is "hoping and praying he'll be on the plane" when the Scots fly to the United States on Sunday.

Gilmour started at Hampden but was withdrawn after pulling up with a knee issue.

His replacement, Findlay Curtis, scored Scotland's first-half leveller before Lawrence Shankland's double after the break and a late Ryan Christie penalty.

"One request was obviously no injuries," Clarke said. "Obviously, we've lost Billy and we're not too sure how bad it is just now.

"I think he's going to his auntie's wedding tonight. He's obviously going to be assessed overnight and fingers crossed the wee man's fine.

"I'm 100% worried. He hurt himself in the tackle and then he made the decision he had to come off, so that tells you that he himself knew it wasn't right.

"We'll just have to wait and see, there's no point in speculating or thinking the worst, let's wait and see what the medics say."

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Midfielder Tyler Fletcher was given his Scotland debut as a half-time substitute and Clarke has confirmed the 19-year-old is one possible replacement for Gilmour.

The Manchester United player – son of former Scotland captain Darren – is one of four youngsters that have trained with the squad this week.

None of those are part of the squad for the World Cup matches against Haiti, Morocco and Brazil, and neither are Rangers' Conor Barron, Andy Irving of Sparta Prague and Udinese's Lennon Milller, who Clarke also named-checked.

"Those three are on standby and obviously Tyler joined us this week," he said. "He's trained well this week, so he's a little bit closer than the other three, but I'd need to have a big discussion with my staff and decide the best way to go."

Fletcher – whose twin Jack plays age-grade football for England – made his senior debut for his father's former club in February and also came on in the final game of the season against Brighton.

Former Scotland winger Neil McCann put it to Clarke on BBC One Scotland that he looked "really accomplished" in a holding role.

Clarke responded: "Everybody was impressed – the players were impressed, the coaching staff were impressed, I had no doubts.

"I actually thought about putting him on as Billy came off but I just thought I'd have a little look, see how the game panned out before introducing him at half-time."