GLENDALE, Ariz. -- Their names are Humber, Leesman and Harrell, and no, this is not a Michigan Avenue firm in Chicago with a tax law specialization.

This trio of pitchers hovers in roster limbo as Cactus League action begins Monday afternoon at Camelback Ranch, with the White Sox visiting the Dodgers at 2 p.m. CT.

Lucas Harrell follows Gavin Floyd to the mound on Monday, and Phil Humber does the same at home Tuesday behind Mark Buehrle. Charlie Leesman had his two intrasquad innings rained out on Sunday, but White Sox pitching coach Don Cooper said he will be rescheduled during the week.

They don't know if the next few weeks of competition ultimately is directed toward filling in as the fifth starter during April, to become the White Sox long reliever or to still get a ticket punched back to the Minors. That scenario will be configured once the White Sox know if Jake Peavy and his reattached lat muscle break camp with the team as the fifth starter and whether the White Sox keep six or seven relief pitchers. Sunday comments from Ozzie Guillen made it seem as if he was leaning in the direction of seven relievers.

In the interim, this trio will be doing whatever it possibly can to impress the White Sox. As Cooper recently said, it's the pitchers who provide ammunition to continue to be sent out there over the next four weeks.

Brian Bruney, Gregory Infante, Anthony Carter, Jeff Gray and Miguel Socolovich stand as a few other hurlers who would like to have a say in that last open relief spot. But here's a brief look at all three of these primary bubble candidates, who are the best fits to slide between spot-starting and long relief.

Phil Humber

The right-hander who played an integral part in Rice University's 2003 national championship faced enough pressure simply coming into the game with the New York Mets as the third pick in the 2004 First-Year Player Draft. Add to that equation being part of the 2008 trade for Johan Santana, the game's best pitcher at the time, and the expectations for success wore quite heavy on Humber's shoulders.

With a 2-1 career record and 5.26 ERA, Humber hasn't come near those lofty expectations. But he had a different feeling about his approach over eight games, including one start, with Kansas City last year.

"Last year, nobody expected anything of me," Humber said. "I was signed as a Minor League free agent, and it's not like reporters were standing around my locker. It was nice for me just to back away from that kind of thing.

"I was doing it for me, not because someone else is expecting something out of me because of this or that. I'm better for it. And if something like [high expectations] would happen again, I'll be more prepared. Part of it is maturity and knowing yourself and what you are capable of doing."

As for keeping an eye on the roster bubble or whether he fits as a starter or a reliever, Humber just doesn't worry about such matters. He's ready to make a strong Cactus League impression through his debut against the Brewers.

"If there's a spot for me, whether it comes as a starter or in the bullpen, I feel like I'm capable of doing either one," said Humber, who was claimed off waivers from the A's on Jan. 18. "Hopefully, I'll put my best foot forward and have a chance to help the team. And if you can help a team like this, you feel like you're doing something. This team is going places this year."

Lucas Harrell

There was a time about four years ago when Harrell was thinking about getting out of baseball. He missed the entire 2007 season after undergoing surgery on his right shoulder in January and really didn't feel close to 100 percent until pitching for the gold-medal winning Team USA in the 2009 IBAF Baseball World Cup in Italy. Harrell didn't allow an earned run over 10 innings in the competition, all coming in relief.

Harrell finished 12-4 with a 3.27 ERA over 25 starts between Double-A Birmingham and Triple-A Charlotte during that same season.

"After my surgery, there was a point where I doubted a little bit if I would get back to 100 percent," said Harrell, who mentioned that coaching would have been his next profession if he left baseball. "If I was not at 100 percent, I wasn't going to be able to help the organization.

"Getting my confidence back was a huge key. I pitched against Cuba, and they said Cuba would be like a quality professional team, and that gave me the boost of confidence I needed."

Statistics from 2010 indicate Harrell might be better served as a reliever than a starter. Harrell finished 1-0 with a 6.28 ERA as a starter but posted a solid 2.79 ERA out of the bullpen. In a spot start on July 30, Harrell gave up just four hits over five innings and struck out one but still picked up his lone big league decision in his debut during a White Sox victory over the A's.

Working within the strike zone is important for the sinkerball pitcher.

"Ground balls and getting hitters to make contact are important," Harrell said. "I can't walk a lot of people because I won't strike out a lot."

Charlie Leesman

An eye-opening effort during Spring Training a year ago earned notice for the young left-hander from none other than Guillen. Leesman, who turns 24 on March 10, followed up that showing with a 14-6 record between Birmingham and Class A Winston-Salem, but he also walked 66 in 148 1/3 innings.

Leesman stands as the longest shot of this trio to break camp. He almost certainly won't be considered for solely a long-relief spot.

"We'll probably still continue to start Charlie," said White Sox Minor League director Buddy Bell. "It will be interesting to see what he does this spring in terms of command. If it's consistent, you could put him in that group. Not at the top, but he's an option."

Leesman worked regularly for the first time out of the bullpen during the Arizona Fall League, appearing in 11 games but finishing with an 11.81 ERA.

"I've been in the bullpen a couple of times, for short stints here and there," Leesman said. "But the Fall League really gave me that feeling of making that bullpen adjustment."