While he attended the final as an injured player, Casemiro missed the celebrations after United defeated Manchester City 2-1 at Wembley.
Casemiro was replaced in the matchday squad by defender Willy Kambwala due to injury.
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United manager Erik ten Hag said of his absence: "Cas is not 100 per cent.
"Also we want in that space around Phil Foden, we need a strong defence."
The Sun says Casemiro missed the partying to leave the country with his family on their summer holiday.