Millwall chairman John Berylson will not risk the future of the club in pursuing promotion to the Premier League.
The Lions announced losses of £4m for the last 12 months, up £3.4m on the previous year, but Berylson has made a further £8.5m available over the next three years.
"This is a long-term plan and I am delighted the club is making progress on and off the field," said Berylson.
"The regeneration of the surrounding area at The Den and our commitment to the Millwall Community Scheme shows we are here to stay.
"Too many clubs have gone through boom and bust to get to the Premier League. Millwall is committed to getting there in a sensible way.
"Developing The Den and our surrounding area will help to future proof our prospects and success."