The Scottish Premier League insist they will have no choice but to extend the season if Rangers reach the UEFA Cup final.
Celtic chief executive Peter Lawwell last month claimed an extension would 'threaten the integrity' of the competition, while maintaining that his club had plans for a tour to Japan.
But today the SPL published two provisional fixture lists, one of which sees a four-day extension of the Clydesdale Bank Premier League season to May 22 for clubs in the top six.
Either way, quadruple-chasing Rangers, whose outstanding fixtures against St Mirren and Motherwell have caused the confusion, will play on the Tuesday and Thursday in their final week of SPL action.
And should they beat Fiorentina to make the Manchester final on May 14, they will then have four games to play in eight days, culminating in the Scottish Cup final against Queen of the South on May 24.
SPL chairman Lex Gold, who composed the schedules with secretary Iain Blair, expected complaints.
Gold said Rangers had not asked for an extension and added: 'We have had phone calls from some clubs saying 'well done'.
'We have had phone calls from some clubs complaining they may lose out financially if the last game is midweek.
'I would expect Rangers to be unhappy about the extension not being longer.
'If we were to extend beyond the Scottish Cup final we would be having the bulk of our clubs in the top six waiting 17 days for a game. In terms of the integrity of the competition, that is not acceptable.
'Rangers are also going to be unhappy because of the number of games they have to play if they don't reach the final.
'Celtic have made it clear through the press that they expect the season to be completed before May 18.
'We have tried to be fair to the integrity of the competition, fair to our clubs and fair to the fans.'
Lawwell highlighted his concerns before Rangers progressed further in the UEFA Cup and Scottish Cup.
'You counter that argument because the integrity of the competition is assured by playing games in a reasonable amount of days,' Gold said.
'There are not enough days in the week to get our competition finished if Rangers go through to the final of the UEFA Cup.
'We have got to provide them with as good a chance as possible, as we did with Celtic.
'We could play one of the games two days before the UEFA Cup final. But the league and the Scottish footballing nation should try to help our clubs in Europe.'
When Celtic made the UEFA Cup final in 2003, the SPL moved forward their penultimate game to give them seven days' preparation.
But the Parkhead club had made a complaint over the scheduling of the final Old Firm game three days after their semi-final second leg at Boavista.
'We were able to bring forward the Dundee game before the UEFA Cup final,' Blair said. 'That benefited Scottish clubs in Europe for a number of years.'
St Mirren would also have a three-day extension to their campaign should Rangers beat Fiorentina, with their home game against Walter Smith's men pencilled in for Tuesday, May 20.
Saints chairman Stewart Gilmour has previously stated that his players planned to go on holiday immediately after their season, which had been due to end on May 17.
Gold said: 'We have already had a conversation with Stewart but it wasn't on that territory.
'There are clubs who have more impact on them that have been in contact saying it's the right decision.'
There was little public reaction from the affected clubs but Rangers coach Ian Durrant believes Walter Smith's side must meet their hectic season finale head-on.
He said: 'We have built a big squad and we have got to cope, we can't do anything about it. It is a measure of our success this season.'
And former Celtic player Joe Miller said: 'I think it's acceptable, you can't knock the decision because there's a Scottish club trying to reach a European final.
'If the shoe was on the other foot I'm sure Celtic would appreciate the decision.'