The Manchester United star was in the penalty area as a corner was whipped in in front of the Stretford End, with the bobbling delivery evading everyone at the front post.
Standing in the middle of the six-yard box, Casemiro had an open goal in front of him but somehow got his header all wrong and sent his effort wide of the mark, much to the astonishment of fans in attendance.
That could could have seen the Red Devils draw level after goals from Taiwo Awoniyi and Willy Boly put Forest 2-0 up inside four minutes, before Christian Eriksen clawed one back.
Speaking on talkSPORT's commentary, Ian Danter said: "How on earth did that not get turned in by Casemiro?
"He was a yard in front of goal, it bounced right in front of him but he just couldn't stretch his neck muscles to apply the finish and remarkably, it remains 2-1 to Nottingham Forest."
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Ex-Premier League striker Dean Ashton couldn't believe what he was seeing either, asking: "Did he just close his eyes?
"How has he missed this? It misses everyone, Casemiro's there, Turner doesn't even flick a hand out so it's not like that has put him off.
"He's three yards out with the goal at his mercy and he's put it wide!"
Thankfully for the £70million man, he did make up for his error in the second half after finishing off a great team move involving Marcus Rashford and Bruno Fernandes, drawing the game level at 2-2.
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