Onana was stretchered off after just 20 minutes of Belgium's 4-1 2026 FIFA World Cup win over co-hosts in the last 16 stage with Villa and Red Devils fans fearing the worst.
Belgium's passage into the quarter finals was overshadowed by Onana's injury and head coach Rudi Garcia confirmed a serious knee injury for the 24-year-old.
"We fear it's a serious injury. This isn't good news for him or for us as a team."
The Athletic's David Ornstein has since offered an update indicating an ACL rupture for Onana which will likely mean a minimum of nine months out of action for the former Everton midfielder.
Onana swapped Merseyside for Villa Park ahead of the 2024/25 season, as part of a £50M transfer deal, and he featured in 12 of Villa's games on route to their UEFA Europa League title win in May.
Alongside a fresh headache for Unai Emery's squad plans, it could now also change his transfer objectives, with the Spanish coach previously happy with his midfield options.
Emery may now dip into the market to sign cover for his engine room and it could stiffen Villa's stance over letting Morgan Rogers join Arsenal in the coming weeks