Manchester United Supporters' Trust (MUST) has sent an open letter to the club over Jose Mourinho's issue with the Old Trafford atmosphere.
Mourinho labelled the stadium "quiet" after United's 2-0 win over Huddersfield earlier this month, prompting MUST to defend the club's supporters, insisting it was "an issue affecting clubs throughout the country".
MUST recently met with club officials for an initial overall discussion over issues affecting fans at games, and has outlined short to medium term solutions to United as "stadium expansion is essential in the longer term to deal with the major challenges which exist".
In an open letter to group managing director Richard Arnold, MUST said: "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."