Richard Arnold has vowed Manchester United will be relentless in their efforts to arrest the team's drastic decline.
United ended a fifth consecutive campaign trophyless and fell from second to sixth when they were recognised as would-be title challengers at the start of the season.
Former manager Ole Gunnar Solskjaer was sacked in November and the club suffered FA Cup fourth round and Champions League round-of-16 eliminations under interim manager Ralf Rangnick.
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United will compete in the Europa League for the fifth time in the last eight seasons in 2022-23 and Rangnick, now a consultant, likened the squad rebuild to 'open heart surgery'.
New manager Erik ten Hag highlighted United's misleading second-place finish last season but supporters are demanding a significant overhaul of a squad that under-performed so wretchedly United matchgoers chanted 'You're not fit to wear the shirt'.
"Suffice to say, we are not happy with where we are in terms of performance on the pitch," Arnold said on the fans' forum. "We understand fans are frustrated and want to see change and improvement. I can assure you that we share that frustration very intensely within the club.
"But we also feel confident that change is coming because of the action being taken to drive long-term success. The appointment of Erik ten Hag was the most visible example of that action, and the most important. We’re pleased to have got that done early and we can't wait for Erik to get started.
"Success won’t be achieved overnight but we are determined to get there, and we will be relentless in our efforts to achieve it. The support of fans will be crucial, and we accept that we have further work to do to strengthen that relationship, aided by the work of this Forum."
Arnold was also asked about the toxic atmosphere that marred some of the final home games of the season, with thousands of supporters protesting against the ownership of the Glazer family.
Co-chairman Avram Glazer admitted this week: "It is a disappointing season and we're gonna work hard to make next season a better season."
In response to the fan's question, Arnold replied: "As stated earlier, everyone at the club, from the owners down, accepts that performances this season have been well below what we expect. We are taking decisive action to improve things and there is huge commitment and passion across the club to return to where we think we belong – challenging for, and winning, titles.
"We are very aware of how fans are feeling and understand their concerns and frustration. Football is a game of passion and we fully respect fans’ right to make their feelings known, as long as this remains legal and peaceful at all times.
"We have a duty of care to the fans who come to enjoy games, and to our staff who enable games to go ahead, and their safety will always be our priority. I would very much hope that all fans within Old Trafford approach next season with renewed optimism and confidence as we look forward to a fresh start under Erik ten Hag.
"We have the best fans in the world and when Old Trafford is at its loudest we have a significant advantage against our opponents. I hope this unrivalled passion will be used to support the team and the new manager as we start this exciting new chapter together."
