A date has yet to be set for Rousey, the recently signed women's bantamweight champion, to make her UFC debut, promotion president Dana White said Saturday night.
Rousey is the first and only women's mixed martial artist under contract with UFC, though White says efforts are being made to bring on more 135-pound fighters.
An effort was made to sign Santos, a former Strikeforce featherweight champion, but thus far she is unwilling to drop to 135 pounds and fight Rousey in a highly anticipated bout.
"I haven't talked to (Santos') camp, but our matchmaker has and she doesn't seem too excited to fight Ronda," White said. "We're bringing in the 135-pound division.
"That's what we're doing. I'm trying this whole women's thing out."
UFC intends to only promote the women's bantamweight division at this time. Santos' reluctance to fight at 135 pounds means that she will not compete in UFC in the foreseeable future.
Santos has not fought since Dec. 17, 2011, when she defeated Hiroko Yamanaka by first-round TKO. The result of that fight, however, was overturned after Santos tested positive for stanozolol, an anabolic steroid.
Santos was stripped of her title and suspended for one year.
When an opponent is found for Rousey it is possible that she will defend her title in a UFC main event. White said Rousey's debut will be on a pay-per-view card.
"She's the champ," White said. "Unless there's a (men's) weight division higher than (bantamweight) and she's defending the title, she'd be the main event.
"She is the first ever UFC women's champion."
Rousey (6-0) won the Strikeforce bantamweight title with a first-round armbar submission of Miesha Tate on March 3. She successfully defended the title in August with a first-round armbar submission of Sarah Kaufman.