Jankewitz, 19, was sent off in the second minute of the game for a rash tackle on Scott McTominay which reduced the Saints to 10 men as United ran riot and equalled the Premier League record for the biggest margin of victory.
“Abuse of any form will never be tolerated at Southampton,” the club said in a statement.
“Our club prides itself on its inclusive nature, and supporters who stoop to such abhorrent and archaic standards are not welcome as Southampton supporters, or anywhere else within football.
“The club will continue to fight every day to remove such people from our sport and our community.”
The south coast club said they were passing on all abusive messages to the Hampshire Police in the hope that the guilty individuals are permanently removed from the football community.
Southampton have lost their last four league games and are 12th in the standings with 29 points. ― Reuters