Celta Vigo have told ESPN FC that Manchester United have not made all of their allocated tickets for their Europa League semifinal return leg at Old Trafford available to them and will ask UEFA to take action.
Article 36 of UEFA'S competition regulations state that home clubs must make at least five percent of the total approved UEFA capacity of their stadium available exclusively to visiting supporters.
United's Old Trafford is the biggest club ground in the Premier League with a current capacity of more than 75,000.
The Liga club confirmed they have only received 1,900 of 3,780 tickets they are entitled to for the encounter in Manchester on May 11 and attempts to resolve the issue have so far proved unsuccessful.
"A meeting took place with United in Manchester yesterday [Wednesday] but the ticket issue has not been resolved," a Celta spokesman told ESPN FC on Thursday. "Celta are demanding United to hand the remaining tickets that the club is entitled to.
"If the situation is not resolved in the next few days, we will have to ask UEFA to intervene."
Later on Thursday, sources close to United said they offered Celta Vigo a full allocation of 3,000 tickets only to hear back from the Spanish side in writing that they only required 1,900. United then sold the remaining tickets to supporters.
The United sources insist the club acted in accordance with UEFA rules and are confident there will be no case to answer if Europe's governing body get involved.
Earlier on Thursday, Celta announced that all general tickets for next week's first leg against United have sold out less than 48 hours after public sale began.
�� Balaídos se llenará ante el @ManUtd: entradas agotadas.
➡️ https://t.co/CkRqorYgbJ pic.twitter.com/WH1YErfdb5
- RC Celta (@RCCelta) April 27, 2017
The Spanish side, who hosts the first leg of the tie at their 29,000-seat Balaidos Stadium in Vigo next Thursday, said in a statement: "Balaidos assures itself the best of Celtista atmospheres for the historic Europa League game against Manchester United.
"On Thursday, the ticket office at the stadium put the sold-out signs for all the stands."
Celta eliminated Ukrainian team Shakhtar Donetsk and Russian side Krasnodar before drawing 1-1 at Genk last week to advance to the last four of the Europa League with a 4-3 aggregate win.
Winners of the Intertoto Cup in 2000, Celta have never played in a semifinal of a major European competition before and square off against United in European competition for the first time.