And Deans insists his side will require the extended mid-season Super Rugby break in order to avoid a disastrous series.
"That (not having five weeks) would obviously be a recipe for disaster," said Deans.
"It (the Lions series) is an important moment in every rugby player's life - once in every 12 years they get this opportunity.
"We need to do the right thing by the playing group and ensure that they get the preparation that's required to win. Anything short of that is negligence."
Deans reckons the Lions will have a distinct advantage in terms of preparation, with six matches ahead of the first Test.
"They've got a great run - we've just got to ensure that we don't compromise," added Deans.
The Australian Rugby Union have begun negotiations with their SANZAR partners to arrange a workable schedule.
And New Zealand and South Africa could return to Super Rugby action ahead of the Australian sides.
"The window here in Australia needs to be wider than it necessarily will be for South Africa and New Zealand, because we have the Lions arriving early June and they are here till early July," said O'Neill.
"We need not a three-week window - we need a five-week window. "
"It means South Africa and New Zealand could well resume Super Rugby without us and play their derbies."