But outfielder/first baseman Nick Swisher, who lockered next to Thomas last spring and hung on the Big Hurt's every word throughout the season, thinks the A's remain well-stocked when it comes to powerful, positive presences.
"We've still got all kinds of leadership," Swisher insists.
Asked to identify said leaders, he's quick to respond.
"That's easy, man. Mark Kotsay, Jason Kendall, Eric Chavez," he says. "Between those three guys, we've got everything leadership-wise a team needs."
Kotsay, Kendall and Chavez have 30 years of big-league experience between them, with Kendall's 11 making him the longest-tenured of the trio. And Swisher says each man brings a little something different to the table.
"Kotsay's the most vocal-guy leader; if something needs to be said, he'll say it, and he won't have any problem saying it," Swisher offers. "He's taught me a lot about the right way to play the game. Kendall, he's a lead-by-example guy more than anything. He's the ultimate gamer, out there every day, nose to the grindstone, battling, always showing you the way the game's supposed to be played."
And Chavez? There was a time when few would consider himself a team leader, but times have changed. Since making his famous "bus speech" in Washington, D.C., during the 2005 season, he's been steadily growing into a new role.
"He's been the face of the franchise for how long? That right there has to count for something," Swisher says. "But that's not all he is. He's kind of in the middle of Kotsay and Kendall. He's definitely gotten more comfortable speaking up since I've been here, and the way he plays through injuries and everything, that's kind of by-example leadership, too.
"They're all different, but together they're perfect for this team."
Adds first-year manager Bob Geren: "We lost some guys with those [leadership] qualities, but it's still a very strong clubhouse in that sense. I don't think there's going to be any kind of void."
Geren and others admit, however, that while there are plenty of leaders among the position players, there isn't an obvious successor to Zito, who was the unquestioned leader of the pitching staff.
"I think only time will tell with that one," says closer Huston Street.
Geren and Street both pointed to Esteban Loaiza's 12 years in The Show, figuring he'll take on a larger role in his second year with the team. But Street doesn't think the responsibility has to fall to a single member of the staff. He sees it as a group effort.
"The great thing is that we have a lot of guys who kind of came in together, kind of like the Big Three did," Street says. "[Tim] Hudson, [Mark] Mulder and Barry came in pretty much together, and they became like a unit instead of three individuals. A couple of years ago, in 2005, we had something similar. Guys like Dan Haren and [Joe] Blanton and [Kiko] Calero and myself all had their first big year [in the Majors] at the same time, and I think that's something that brings guys together as a group. And Rich Harden was here before us, but he's a young guy, too.
"So I don't think it has to be one guy like it was with Barry. Don't get me wrong, Barry was incredible at it. But we don't have a guy like Barry right now, and that's OK, because I think we have a bunch of really good guys whose strength is going to be as a unit."
One of Zito's strengths, Haren has said, was his ability to prop up fellow pitchers whose confidence had been shaken. Street confirms as much, and several teammates have suggested that Street himself is the best candidate to take on such duties.
"That's a great compliment," he says. "And I'd love to be that guy. Barry was always there for you, and that's the kind of teammate I want to be, too. It's not always easy to be that guy, but it's important to have someone like that. I don't know if I'm the perfect guy or not, but I'll definitely be there if someone needs me, absolutely."
The questions about how the A's will take shape on the field won't be answered for quite some time, perhaps not even by the end of camp. The hope is that a healthy Harden will ease the pain of losing Zito, and that the addition of Mike Piazza and stronger years from Chavez, Kotsay and shortstop Bobby Crosby will make up for the loss of Thomas and Payton. Another six months of production similar to what Bradley provided after the All-Star break last year will help, too.
But there are no internal questions about leadership. The A's aren't thinking about what's gone as much as they are about what's before them.
"It's a new beginning, a new identity," says Bradley. "A new brand of A's baseball."