Demand for tickets and commercial deals is likely to drop unless prices are reduced, meaning clubs can expect less revenue next season than this.
"Season tickets, corporate hospitality and commercial sponsorships were all negotiated a year ago," Mawhinney told BBC Five Live.
"They're about to start doing that for next season and there will be a reality check for some clubs."
English clubs collectively are £3billion in debt - though this figure is skewered by the massive debt run up by Premier League clubs such as Manchester United, Chelsea and Liverpool.