Although we've long known that Scarlett Johansson's Black Widow won't be the only female character in The Avengers, there's been little indication who might help to provide a little balance to a testosterone-heavy lineup. Director Joss Whedon has only said there will be just one female Avenger, meaning no Wasp or Scarlet Witch -- in costume, at least.

But on NBC's Late Night With Jimmy Fallon, Samuel L. Jackson gave hope to fans holding out for a role for SHIELD agents Sharon Carter, Carol Danvers or Maria Hill. What's more, he indicated that Nick Fury will appear in Thor after all.

"I gotta screen test like five actresses on Friday," he said last night. "They have this new character that I guess is my sidekick or something that's with me all the time. So they're auditioning girls for it."

Fallon gasped, saying, "Some secret, good stuff. If we were at Comic-Con, there'd be a riot right now." (Watch the interview segment below.)

Sharon Carter seems the most likely candidate for Fury's "sidekick," as the character (aka Agent 13) has a lengthy history as a SHIELD operative. Perhaps just as importantly, in Marvel comics she has significant connections to Captain America: She's his one-time girlfriend of Captain America, and the niece of his World War II-era love interest Peggy Carter (played in Captain America: The First Avenger by Hayley Atwell).

That said, we shouldn't discount the possibility of Carol Danvers, potentially laying the groundwork for Ms. Marvel to appear in an Avengers sequel, or Maria Hill, the SHIELD director turned Avengers leader.

Jackson, who confirmed his nine-movie Marvel deal, also revealed that he'll shoot his Thor and Captain America cameos "in the next month or so." The actor had previously said he wouldn't appear in the Kenneth Branagh-directed Thor, which opens on May 6.

"Thor and Captain America are pretty much done, but I haven't done my part in them yet," he said. "I'm just connective tissue for them to join the Avengers."

He confessed that he doesn't yet know where in those two films his part will fall.

"I don't know, I have no idea what they want me to do," Jackson said. "It was so funny, because when I saw Iron Man for the first time, I sat there and they had the film -- they screened the film for me, my agent and some other people were sitting there, the credits came and went and I wasn't there. They sent the wrong print! Then they sent a dude to my house with like 30 seconds of film. I had to watch and sign something, then he had to leave."

The Avengers, which also stars Robert Downey Jr., Chris Evans, Chris Hemsworth, Mark Ruffalo, Jeremy Renner, Samuel L. Jackson and Clark Gregg, opens on May 4, 2012.

Update: Five actresses have emerged as the lead contenders for the role of Fury's "sidekick."