Channel 4 could need as much as £150m invested by 2012
The chief executive of Channel 4 has said he would oppose a merger with Five, saying it would be like "mixing oil and water".
The future of Channel 4 is to be decided in the next few weeks.
Discussions have been held between its management, regulators and the government over how to replace falling revenues from advertising.
C4's Andy Duncan said he believed a merger with the BBC's commercial arm, BBC Worldwide, could be the answer.
It is thought a possible merger with Five is just one of the options for Channel 4 in the upcoming government report on ways to overhaul public service television.
A draft report by communications minister Lord Carter will offer a number of proposals for the broadcaster, which said it could need as much as £150m invested by 2012.
The options also include offering it some of the BBC's licence fee.
Andy Duncan told BBC Radio 4's Today programme that a merger with Five was not the answer.
"Mixing us with Five - who are a for-profit company, they want to maximise money to go back to their foreign owners - is very difficult. I think it is like mixing oil and water."
He believes a tie-in with BBC Worldwide could offer the best solution for Channel 4, which is a publicly-owned and not-for-profit.
"We believe and I think the BBC believe - there is just a difference as to how much money might be there - but we both believe that by working more closely together these two public organisations can make those public assets work harder, create more money to put back into the system to spend on content," he said.
"We think that is a very interesting part of the solution, possibly the whole solution."
Merger talks between Channel 4 and Five were held in 2004, then called off because of the complexity of combining the public and commercial stations.
Discussions were started under Channel 4's former chief executive Mark Thompson, who then left to become director general of the BBC.