Clubs outside the Premier League cannot resume training till "May 16 at the earliest" due to the coronavirus pandemic but the season can be completed in "56 days" English Football League chairman Rick Parry informed them in a letter.
The 72 clubs have been kicking their heels since the EFL suspended the campaign in the Championship, League One and Two on 13 March.
All 24 sides in the Championship still had nine matches to play.
Some clubs in League One have 12 games remaining, while in League Two, teams have either nine or 10 matches remaining to complete the regular season.
However, Parry said following a EFL board meeting on Thursday they were confident once there was a resumption the league fixtures and the promotion play-offs could be completed within two months.
"The EFL Board today determined that to provide a level of certainty, clubs should not recommence any training activity with players until May 16 at the earliest," Parry wrote.
"Whenever the decision is taken that it is safe to resume, we currently estimate that the League will require 56 days approximately to complete the outstanding matches in the season (including Play-Offs)."
Parry said it is probable the matches will be played behind closed doors due to the British Government's social distancing measures.
"It is our working assumption at this stage that matches will be played behind closed doors when we eventually return," he said.
"As part of our contingency planning we are absolutely mindful of the need to try and mitigate the cost of this to clubs as best we can."
The financial fall-out has been raised in stark terms by FA Chairman Greg Clarke earlier this week warning that unless football united behind a plan clubs and leagues could disappear.
Several sides have already put players and staff on furlough or temporary leave whilst players of Championship table-toppers Leeds United have agreed to a deferment of their wages.
Parry's letter suggested the delayed resumption of the present season could impact on the start of the 2020/21 campaign.
"Looking more long-term, the EFL must remain mindful of the implications that the extension of this season may have on the commencement of the 2020-21 campaign," he said.
"We will ensure there is a suitable break between the two, so as to allow clubs and staff sufficient time to regroup and prepare accordingly.
"I think there will be a sigh of relief as and when we reach that point."