UFC president Dana White says he spoke to the welterweight champion earlier this week, and St-Pierre expressed he has "unfinished business" with Diaz.
The two were scheduled to fight at UFC 137 in October 2011 and UFC 143 in February but have yet to meet in the Octagon, mostly because of the champ's torn ACL.
St-Pierre (23-2) returned to action last month with a unanimous decision win over Carlos Condit in Montreal. Expectations were that he next would face middleweight champion Anderson Silva in a proposed "super-fight."
White says he feels obligated to grant St-Pierre's request to fight Diaz, even if it means postponing the dream matchup.
"Georges St-Pierre has been a phenomenal champion," White said. "He's a great guy to deal with and he doesn't ask for things. So, if he wants to fight Nick Diaz and Nick Diaz wants to fight him, then that's probably the fight we'll make."
White said he did have a possible date in mind for the fight, but declined to reveal it.
Diaz (26-8) is currently serving a yearlong suspension stemming from a failed drug test in February, when he tested positive for marijuana metabolites following a decision loss to Condit.
One name left out in the news is that of welterweight contender Johny Hendricks. The former collegiate wrestler is riding a five-fight win streak, including a 46-second knockout of Martin Kampmann at UFC 154 last month.
If St-Pierre does fight Diaz next, White said he'd likely force Hendricks to fight another opponent as he waits.
"Listen, Johny Hendricks has had some great fights," White said. "When you talk about winning in spectacular fashion -- this guy hits people so hard they skid across the Octagon.
"He's in no position to demand anything (though). Georges St-Pierre is the champ. He has been forever. If that's the fight he wants, that's probably the fight we're going to give him if Diaz accepts it."
No backup opponent was mentioned for Silva (33-4), although White said he recently met with the Brazilian and that "fun things" were discussed for him as well.
The UFC figurehead also ventured to guess the 37-year-old Silva still would get in a fight with St-Pierre and current light heavyweight champion Jon Jones before his career is finished.
"He'll fight anybody," White said. "And he knows he'll win if he does."