Manchester United co-chairman Joel Glazer says the club "apologise unreservedly for the unrest" caused by the proposed European Super League.
United, Liverpool and four other Premier League sides withdrew from the ESL on Tuesday after a backlash.
"We failed to show enough respect for its deep-rooted traditions," Glazer said in an open letter to fans.
The 50-year-old admitted efforts "in seeking to create a more stable foundation for the game" did not honour the conventions of promotion and relegation within the wider football pyramid.
"For that we are sorry," he said. "This is the world's greatest football club and we apologise unreservedly for the unrest caused during these past few days.