The Tricky Trees and Clarets played out an entertaining 1-1 draw but things ended very badly for the young striker.
With time ticking away, Foster threw an elbow into Ryan Yates' ribs off the ball.
The referee, Robert Jones, missed it. But VAR didn't, and he was sent off.
And now Burnley are set to be without their top Premier League goalscorer for some big games.
When will Lyle Foster return for Burnley?
Foster was sent off for violent conduct, meaning he faces a three-game domestic ban.
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The 23-year-old didn't deny a clear goalscoring chance, so unless the ban is overturned on appeal, the Clarets are set to be without a key player in Foster.
Foster will miss Saturday's game at home to Manchester United, live on talkSPORT.
He then will be unable to play in the Carabao Cup tie against Salford City before missing Burnley's trip to St James' Park to face Newcastle.
This means he will return for the Clarets' huge game against Luton on Tuesday, October 3.
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So, despite getting sent off in the Premier League, Foster will only miss two top-flight matches because domestic red cards are served across all competitions.
Speaking after the 1-1 draw with Nottingham Forest, Vincent Kompany refused to criticise his striker.
He said: "When you see the gesture on the screen; it's a moment of inexperience.
"It's something that we can't really excuse, but at the same time, he's played his heart out for the team.
"We need to be there for him."
Foster had earlier seen a goal ruled out for what was deemed to be a deliberate handball by Burnley teammate Sander Berge in the build-up to him tapping home, so it was definitely an evening to forget.