Among those still in the running for the final two bullpen spots are lefties Jorge De La Rosa and T.J. McFarland along with righties Michael Blazek and Kris Medlen.
McFarland is the only one of the four on the 40-man roster, while De La Rosa is an XX(b) player, meaning that by Saturday, the team had to add him to the roster, pay him a $100,000 retention bonus or release him.
"The choices are we have to either grant him his release, or he can stay in the organization if we pay him the retention bonus or he makes the team," general manager Mike Hazen said. "Or we have to add him to the 25-man roster. I don't have an update on that right now. He is obviously still here. We'll have a formal status update in the next few days."
That would seem to indicate the D-backs are going to keep De La Rosa on the Opening Day roster but don't currently have an open 40-man roster spot for him.
Marrero has played first, second, third and short in his three-year career. His addition could free up infielder Chris Owings to play more in the outfield early in the season while right fielder Steven Souza Jr. is on the disabled list.
"We love his versatility," Hazen said. "He's got great defensive ability, hit left-handers well last year. Great teammate, good baseball player."
The 27-year-old slashed .208/.259/.309 over parts of three seasons with the Red Sox, and he has a career .710 OPS against lefties.
Not quite there
While it's very likely Marrero is on the Opening Day roster, the D-backs aren't committing to that just yet as they continue to explore options to replace Souza in the outfield.
"We're not 100 percent done with everything yet," Hazen said. "We're still looking, exploring."
The humidor at Chase Field is up and running, and the team is hoping to use baseballs that have been in the humidor during the two exhibition games at the stadium Monday and Tuesday but is still waiting approval from Major League Baseball.
"It's not a big deal either way, but if we are allowed to, we will," Hazen said.
Zack Greinke threw a 10-pitch bullpen session Saturday and is scheduled to pitch Monday against the Indians at Chase Field.
If that goes well, he would likely make his first regular-season start Saturday against the Rockies.
The D-backs close out the Cactus League portion of their spring schedule Sunday with a 1:10 p.m. MST game against the Rockies. It is Robbie Ray's day to pitch, but he will likely throw on a back field rather than face a Colorado team that he will start against Friday in the second game of the regular season. Following Sunday's game, the D-backs will play two exhibitions against the Indians at Chase Field on Monday and Tuesday.