Harris Associates, Crystal Amber and Invesco Asset Management have also indicated their support for the bid to raise £65m, subject to conditions.
An agreement has also been reached with its lender Bank of Scotland to provide a new working capital facility of £25m until May 31 2014.
Chief executive Keith Jones said the new credit line and fundraising will provide sufficient working capital for its current requirements.
One of the four investors’ conditions is that the company voluntary arrangement (CVA) proposal for the retailer, masterminded by KPMG, gets the required approval from landlords at a meeting on Tuesday March 22.
Despite the current drop in consumer confidence levels and problems for many retailers, JJB said it had been achieving internal expectations for trading in recent weeks.
Chairman Mike McTighe said: "The next key stage in the process is the creditor and shareholder votes next week. The board remains confident of the success of this turnaround and the future prospects for the company."