The debt has been covered by the club’s American owner Ellis Short, but is likely to prevent the club complying with the impending Financial Fair Play regulations
The Premier League club saw a reduction of losses by £4.3m and expenses from £110.7m to £104.9m on last year’s results, although these figures do not include the £9.5m spent on transfers in January.
Manager Martin O'Neill has also expressed desire to bolster his first-team squad in the summer after flirting with relegation for the majority of the 2012-13 season, and chief executive Margaret Byrne insists money is being spent in the right areas for the long-term sustainability of the club.
"Our results reflect a period where we embarked on a programme of continued investment in the playing squad, choosing to retain the services of those players that the manager identified as key to the team," Byrne told the clubs official website.
"We also invested significantly in our Academy in order to secure EPPP Category One status and give us the best possible chance to develop young players for the future.
"Our net operating loss has reduced slightly and we are continuing to implement a structured financial plan to ensure sustainability for the future."
Sunderland are currently embroiled in a relegation battle at the bottom of the Premier League having failed to win in their last seven league outings, leaving them four points above 18th-placed Wigan with eight games remaining.