The London Mayor, who galvanised Conservatives with his announcement yesterday that he intends to make a return to Parliament, urged the Prime Minister to "go hard into the tackle" in his talks with EU leaders.
Mr Johnson has been accused by some Tories of trying to set a trap for Mr Cameron by using a keynote speech to set an impossibly high list of demands for reform - including renegotiating the Common Agriculture Policy - ahead of a referendum on Britain's EU membership in 2017.
But in a newspaper interview yesterday he insisted that the changes he was seeking should be well within the realms of possibility, provided the Prime Minister was prepared to get tough in the negotiations.
"I'm not so pessimistic. I think you could easily. There is no reason why an IGC (intergovernmental conference) to settle all those points shouldn't be done in that space of time.
"I think it could be done," he said.
He added: "If you don't go in hard to the tackle, you are never going to come out well. You've got to go in hard and low."