Young has had an impressive campaign with the Red Devils, but Jose Mourinho will no doubt be livid if the 32-year-old full-back is handed a ban after the incident at Old Trafford.
The United No.18, one of the club's best performers this season, lashed out at Saints' player Dusan Tadic when marking him on a corner in the second half at Old Trafford.
Young accepted the charge on Sunday and his argument the three-game suspension was excessive was rejected by a regulatory commission.
The incident was missed by referee Craig Pawson and his officials but picked up on TV cameras after the game and Young has been charged retrospectively.More news: Tune in tomorrow for President Buhari's New Year Address
Manchester United wing-back Ashley Young risks a lengthy ban after clashing with Dusan Tadic during their 0-0 draw with Southampton.
United will also be without Romelu Lukaku for the time being after he was stretchered off in the 14th minute of the draw with Southampton.
He also has until 5pm to respond to the charge.