The Manchester United Supporters' Trust (MUST) has urged the club to look into improving the atmosphere at Old Trafford.
Red Devils manager Jose Mourinho labelled the stadium "quiet" after the 2-0 win over Huddersfield Town earlier this month, prompting MUST to defend the club's supporters.
The trust recently met with club officials for an initial overall discussion over issues affecting fans at games, with "dedicated meetings with appropriate staff on key issues" lined up.
In an open letter, MUST has outlined short- to medium-term solutions as "stadium expansion is essential in the longer term to deal with the major challenges which exist".
The letter, addressed to group managing director Richard Arnold, read: "As you know the atmosphere in the stadium is a key issue for supporters and also for the manager and the team.
"While we understand that the issue of stadium expansion at Old Trafford remains under active consideration, and that a firm decision has not yet been made on whether the investment will be made into a significant capacity increase, we recognise the major financial, technological and logistical challenges this presents.
"We acknowledge the positivity of our initial discussions with you and ask that the club continues to work in partnership with supporters in developing plans to the mutual benefit of the club and supporters.
"We are keen to push ahead as quickly as possible on discussion of interim measures which will produce progress while we await the major stadium development that is so badly needed."
Man United return to action this Saturday with an FA Cup fifth-round tie away at Huddersfield.
