The two clubs have been engaged in a price war over tickets which escalated when United informed their travelling supporters their first leg tickets to the Spanish match would be subsidised by charging Sevilla fans more for the second leg.
Sevilla are charging United fans between 89 and 133 pounds ($120 to $179) to watch the game at the Ramon Sanchez Pizjuan on Feb. 21, which the English club considered excessive.
In an email to ticket holders for that game, United explained they would be refunding them 35 pounds, which is the difference between the 89 pound ticket price and the 54 pound price Liverpool supporters were charged by Sevilla during the group stage of the competition.
Sevilla responded by saying they would subsidise their own supporters' tickets to the Old Trafford match and complain to the European football governing body about their fans' allocation of 2,995, which they say is 4.1 percent of the stadium's capacity.
Champions League rules dictate that home sides make 5 percent of the seats available to visiting supporters.
"Sevilla will subsidise the tickets of the fans who go to Manchester by the same amount the prices rise, so they will not pay more than the 60 euros established (by United) in the first place," read Sevilla's statement.
"On top of that we will make UEFA aware that five percent of the stadium is not being made available (to our fans) and the unilateral price rise - after the official request for tickets (from Sevilla) - as well as asking them to verify that Sevilla fans do not pay a penny more than British fans for similar tickets, as per the competition regulations."
A Manchester United spokesman told Reuters: "We are aware of the regulations regarding equal pricing for home and away fans and we will comply.
"We welcome UEFA's willingness to discuss these issues."
($1 = 0.7402 pounds)
(Reporting by Rik Sharma Editing by Jeremy Gaunt)
