Real Betis fans fought with riot police at Old Trafford during the closing stages of their 4-1 defeat to Manchester United.
Trouble appeared to flare up in the away end shortly after Wout Weghorst effectively killed off the tie by scoring United's fourth goal of the game.
A number of away supporters appeared to try and climb over the barrier separating both sets of fans into the home end in the South Stand.
Images show riot police were quick to respond with a line of them getting in between both sets of supporters and preventing any away fans getting into the home section.