The club is very high on De Aza, a 22-year-old who spent last season in Double-A. The question the team is asking itself is whether to hand the starting job to the talented Dominican Republic native, who is widely considered to have the most all-around talent of the candidates available.
Non-roster invitee Alex Sanchez, who started on Tuesday, and Eric Reed are the other choices.
The team still could look at outside alternatives, as rosters are being set around the league, and players without options may become available.
The Marlins open on April 2 at Washington.
Monday's trade for Jorge Julio settled the closer spot, leaving center field, backup positions and the rest of the bullpen to be resolved.
In recent weeks, center field was viewed as a two-player race between Sanchez and Reed. Both are speedy left-handed hitters without much power.
But strong indications coming out of camp on Tuesday made it clear the Marlins may end up making a somewhat surprising decision by giving the job to De Aza.
A lefty hitter and thrower, De Aza played 69 games in Double-A last year, batting .278 with 27 stolen bases and 40 runs scored. He missed time with an injured right hand.
Should De Aza get the nod, Reed would be optioned to Triple-A. Sanchez is a non-roster invitee who has signed a Minor League contract.
If De Aza doesn't make the team, he would open at Double-A, and be available to be promoted sometime during the season.
Other players who have enhanced their chances to make the club are infielder Jason Wood and non-roster invitee reliever Nate Field, who threw a perfect eighth inning on Tuesday.
Tankersley to DL?: On Tuesday morning, Gonzalez gave his strongest indications that reliever Taylor Tankersley will open the season on the disabled list, retroactive to March 23.
Battling back from left shoulder inflammation, Tankersley will pitch in a Minor League game on Wednesday. It will be his first game action of Spring Training. To keep Tankersley eligible to be placed on the DL, retroactive to March 23, the lefty can't pitch in a Grapefruit League game or any exhibition game with paid admission. That means he wouldn't be available to pitch on Saturday against the Reds in Dayton, Ohio.
"We're going to be real safe with him," Gonzalez said. "But we'll see. We'll see what the medical people say.
"This guy is a special guy, and we want him to be with us for a lot of years."
If the team decides to place Tankersley on the DL retro to March 23, the earliest he could see regular-season action is April 7.
Fox arrives: As a player with the Marlins, Andy Fox, wore No. 6. Since that number belongs to Dan Uggla, Fox is wearing No. 9 as the new first base/infield coach.
Hired to replace Perry Hill, who retired on Sunday, Fox was in uniform for the first time as a Marlins coach on Tuesday.
Fox, a former infielder, was preparing to manage the Rangers' short-season Class A club. Those plans changed when the Marlins called to offer the job, which Fox accepted immediately. He then drove 12 hours from Arizona to his home in California, where he quickly packed up and made arrangements to be in Florida to join the Marlins.
Tuesday was Fox's first day coaching for Florida.
"I didn't expect it this late in the spring," said Fox, who played infield in Florida with Hill as his coach. "I didn't know what was going to happen. When they called, it didn't take very long for me to make a decision."
Fox said he has tried to reach Hill, who retired for family reasons, but he hasn't had any luck.
"It's an unfortunate set of circumstances, I don't know exactly what they are," Fox said. "He's a great teacher, and I learned a lot from him. It should benefit me in my new job.
"I think the biggest thing for a new coach is learning the players. Perry has laid a great foundation here, and the best thing I can do is be myself, and keep these guys going on the right path. That's my main objective."
Fox was on the 2003 World Series title team, and he has known a number of people in the Marlins' organization for years.
Now as a coach, Fox is working alongside three men who previously coached him. Gonzalez was the Marlins' third-base coach Fox's first two years in Florida. And hitting coach Jim Presley and bench coach Carlos Tosca were on the staff in Arizona when Fox played there.
Fish bites: Dontrelle Willis will pitch in a Minor League game Wednesday afternoon at Roger Dean Stadium. It will be the D-Train's final spring start, and he is throwing on the back fields to avoid facing the Nationals before he sees them in Monday's Opening Day at RFK Stadium. ... The Marlins turned four double plays at Fort Lauderdale Stadium on Tuesday. ... Aaron Boone, who started at third base Tuesday, had his glove stolen before the game. ... Fox received congratulatory messages from a number of his former teammates, including Mike Lowell, Brian Banks and Jeff Conine, who text messaged him.
Coming up: Prospect Aaron Thompson spent the early part of Spring Training in his first big-league camp. A first-round pick in 2005, Thompson will open the season at Class A Jupiter. On Wednesday, he is making a Grapefruit League start for Florida against Washington at Roger Dean Stadium at 1:05 p.m. ET. Joel Hanrahan will start for the Nationals.