Rob Wilson, football finance expert at Sheffield Hallam University, says the club will have an "acute problem" if they fail to qualify for Europe's premier club competition for a prolonged period of time.
United look in grave danger of missing out on a top-four finish this season following an inconsistent campaign under new manager David Moyes and, despite the club announcing record quarter figures on Wednesday, Wilson warns that their fortunes on the pitch need to pick up.
"Any dip in form will have an impact on financial position and financial performance," he told Perform.
"We would expect to see a net loss of around £30-40 million if they fail to win UEFA Champions League qualification this year, but over the next two to three years if we continue to see this downward trend we would see a big impact.
"If we don't see a sustained two or three years (of failure) then we'll probably see Manchester United come back to where they've been."
Despite revenue from the Champions League making up a small percentage of United's income, Wilson warned that not qualifying would have more serious knock-on effects than to just the finances.
"(The Champions League) is not necessarily a cash cow for Manchester United," he said.
"Based on commercial revenue it's a very, very small proportion of that. It will be very important for them to offer Champions League football to potential players to come in.
"I think if they were to fail to qualify this year it wouldn't have that big an impact this year on what's going on at the football club.
"They can get away with it for the first year but if it was to be sustained where they weren't involved they would have an acute problem."
