Manchester United have written to fans to warn them that the club are at risk of breaching spending rules and ticket prices could rise as a result.
In a letter to fan groups, United said they must "act now".
Under the Premier League's profit and sustainability rules (PSR), clubs can lose up to £105m over three years.
"If we do not act now, we are in danger of falling to comply with PSR/FFP requirements," the club said in the letter.
"We are currently making a significant loss each year - totalling over £300m in the past three years.