The former Dunfermline player and manager is heading a working party who have taken control of the day-to-day running of the financially-stricken club.
Majority shareholder Gavin Masterton announced on Wednesday night he will step down from the board, while chairman John Yorkston is to stand down as chairman and assume the role of honorary president on completion of a share offer, which has so far been delayed.
A sum of £134,000 is owed to Her Majesty's Revenue and Customs, although it is believed the amount is not due to be paid in one instalment.
On the task ahead, Leishman said: "It's the hardest thing I've ever done at this football club, it's the hardest thing I've got to try to achieve.
"Will I do it? I don't know. But I can't do it by myself, that's for sure.
"I've got a short period of time - maybe two weeks, maybe three, maybe four. I've got to remain positive.
"It's about the short-term survival of Dunfermline and the long-term future of the football club."
Some fans staged a protest outside East End Park on Saturday and supporters who had congregated outside the stadium today were invited inside to attend a press conference called to explain the new structure.
Leishman added: "The community of Dunfermline, the supporters of Dunfermline, have been divided. We are not a big enough club to have factions that are going everywhere. We can't be divided, we've got to be together."