Mr Corbyn would become the sixth official candidate for John Prescott's job if he stands.
Today he told Guardian Unlimited: "Nothing's decided until the new year. But there needs to be an anti-war candidate.
"None of the existing ones are. Even [Peter] Hain and [Jon] Cruddas voted for the war."
If the veteran Islington MP stands, it would raise the intriguing prospect of a leftwing "dream ticket" of Mr Corbyn and John McDonnell, who is standing for the leadership.
But both would face a huge obstacle in raising the 44 MPs necessary among the parliamentary Labour party.
The two men are the most rebellious Labour backbenchers, with Mr McDonnell voting against the government 63 times since the May 2005 general election, and Mr Corbyn 60 times.
Mr Corbyn - who is backing Mr McDonnell for the top job - refused to say whether the two men had spoken about a combined ticket, saying merely he had not spoken to the Hayes MP "for a couple of days".
So far the declared candidates are Hilary Benn, the international development secretary, Alan Johnson, the education secretary, Harriet Harman, the constitutional affairs minister, Peter Hain, the Northern Ireland secretary, and Jon Cruddas, a backbench MP.
Mulling over a run are thought to be the leader of the House of Commons, Jack Straw, and the party chair, Hazel Blears.
The contest has yet to truly catch fire, as the cabinet ministers among the runners are refusing to debate until the May local and devolved elections are out of the way.
There is also uncertainty as to when the actual contest will begin. Mr Prescott had promised to stand down when Mr Blair does - at a date which is as yet unknown.
The prime minister has only said that he will leave the job before next year's party conferences.
Mr Corbyn, an MP for 23 years, is a member of the Socialist Campaign Group, and a senior member of the Stop the War coalition.
He is also a member of CND and was a leading campaigner against the Chilean dictator Augusto Pinochet within the UK.
