Despite taking the lead through Zian Flemming’s 10th goal of the campaign, the Clarets slumped to a miserable 4-1 defeat at the City Ground.
A 15-minute Morgan Gibbs-White hat-trick did the damage, before Igor Jesus piled on the misery deep into stoppage time.
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Scott Parker’s side had otherwise been well in the game against a flat and lacklustre Forest outfit, but instantly wilted as soon as the home side applied any pressure.
It means relegation could now be confirmed as early as Wednesday night, when the Clarets host Manchester City.
Here’s how Burnley’s players rated:
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9. Marcus Edwards - 4/10
Involved in the build up to Burnley’s goal, finding himself in space and playing in Hartman. But made it clear he didn't want to track back and help out (Photo by Ryan Pierse/Getty Images) Photo: Ryan Pierse
10. Jaidon Anthony - 5/10
Got in behind on one occasion in the first half but otherwise kept at bay well. Switched flanks but largely made no difference. Photo: Kelvin Lister-Stuttard Photo: Kelvin Lister-Stuttard
11. Zian Flemming - 6/10
Burnley player ratings as 4 and 5/10s dished out after Nottingham Forest misery Photo: Kelvin Lister-Stuttard Photo: Kelvin Lister-Stuttard
12. SUB: Lyle Foster - 5/10
For Edwards, 64 Almost made an instant impact at the back post, with his effort nearly creeping in. But otherwise struggled to get in the game. (Photo by Alex Livesey/Getty Images) Photo: Alex Livesey