Manchester United and Liverpool fans have been urged to behave in a "responsible" manner in a statement from a police chief.
The sides will meet in the second leg of their round-of-16 Europa League match at Old Trafford on Thursday, with Liverpool 2-0 ahead from the opening game at Anfield.
The first leg was marred by chants regarding the Hillsborough disaster -- in which 96 Liverpool fans lost their lives -- which were condemned by United.
UEFA will take no action as the chanting was not mentioned in the officials' reports from the game.
Superintendent Jim Liggett, match commander for Thursday's fixture at Old Trafford, said in the statement: "As always, the TV cameras and media will be focussed on one of the biggest club fixtures in the world and I hope that supporters from both sides act in a responsible manner and enjoy the game, no matter what the result."
After the first leg, United released a statement, which read: "It has always been the position of Manchester United that chants of this nature, which refer to historical tragedies, have no place in the game and do not reflect the values the club holds.
"We are in discussion with our fans' groups to seek their support in preventing this type of behaviour in the future."