Cammy Devlin has been ruled out of contention for Hearts against Kilmarnock.
The Australian midfielder will not feature in the Scottish Premiership fixture this weekend after a head knock on international duty.
Devlin, 24, suffered a concussion in his first start for his country against Ecuador at the Melbourne Marvel Stadium.
The Hearts fan favourite was desperate to play through the pain barrier but was eventually subbed off through precaution by boss Graham Arnold.
Now, Neilson has revealed Devlin suffered a concussion and will be sidelined for the Kilmarnock clash.
The midfielder is due back in Scotland on Friday afternoon but will play no part at Rugby Park.
Neilson said: “He will miss the game at the weekend. He has concussion. He flagged it up with their doctor.
“He was delaying his flight home so he won’t be home until later tomorrow so he will miss the game.”
Devlin had been hailed by international boss Arnold for his willingness to keep playing despite the nasty-looking head injury.
The midfielder required stitches in his head after the collision.
He said: “That’s Cammy’s energy. He had stitches at half time which I was a bit concerned about in the second half.
"He didn’t want to come off but I thought it would be safer.”
Devlin featured for Australia with Celtic's Aaron Mooy unavailable to take up his usual spot in the Socceroos midfield.
And the Hearts star previously admitted he's a major admirer of Mooy - even if he's desperate to get one over on him at club level.
“As a fellow team-mate with the national team, I have nothing but admiration for him," he said.
“I hate saying that when he’s been on the opposing team.
“But I have grown up watching him in the A-League and then the Premier League and as a fellow Aussie I do admire him.
"He’s a great footballer and a great bloke. I just wish we’d got one over him.”
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