"I have to defend against Ruiz because that was part of the deal for me to fight Valuev," said Haye. "Ruiz took money to step aside on the understanding that he would fight the winner.
"So I have to fight him as he is the mandatory challenger and they would strip the title off me if I didn't."
That bout may take place in London, possibly in March next year, but the pair need to overcome injuries first.
Haye revealed that he broke his right hand in his victory over Valuev, while Ruiz suffered a nasty cut during his win against Adnan Serin on Saturday's undercard in Germany.
Leading American promoter Richard Schaefer insists Haye is now the most marketable world champion in the sport.
"Valuev was a great champion and an amazing attraction but today is really the beginning of a new time for the heavyweight division and the sport of boxing," said Schaefer, who is chief executive of Golden Boy Promotions.
"There are a lot of champions and stars out there but really very few who have the talent and skills inside the ring but who can transcend that with their charisma outside the ring.
"And if you were to rank those champions, then the only one at the top is David Haye."
But British promoter Frank Warren does not rate Valuev and believes Haye's quality as world champion can only be judged when he faces one of the Klitschko brothers.
People talk about Valuev like he is something special... he is probably one of the poorest heavyweights ever seen
Promoter Frank Warren
"Nobody can tell me Valuev is a quality heavyweight. He is not even an average heavyweight," said Warren.
"People talk about Valuev like he is something special. He is probably one of the poorest heavyweights ever seen.
"Everybody gets carried away. Just because he is a giant of a man doesn't mean he is a good fighter.
"John Ruiz is a guy who was beaten by Roy Jones. It is when you start talking about the Klitschkos, they are totally different fights.
"They are guys who can box and throw punches. That is when you will see whether Haye can do it at that level. Beating Valuev is not the yardstick."
However, Frank Bruno hailed Haye's bravery in taking on and beating the 7ft Valuev, who had only lost one of his previous 51 fights.
"I thought he had the talent and the speed and ability to beat the guy," said Bruno, a former WBC heavyweight champion.
"It took a lot of guts to come from cruiserweight and fight a man mountain like he did. He stuck to his guns."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.