Dellucci missed last week's games because of left forearm soreness; if he's feeling fine Thursday morning after playing back to back games Tuesday and Wednesday, then outfielder Ben Francisco will be optioned to Buffalo and the roster will be set.
The only other member of the 40-man roster who would have to be taken care of is outfielder Shin-Soo Choo, who is recovering from Tommy John elbow ligament replacement surgery and will open the season on the disabled list. Choo was a designated hitter in a Minor League game for the first time on Tuesday.
Outfielder Jason Tyner, infielder Andy Gonzalez, catcher Yamid Haad and right-hander Brendan Donnelly will be reassigned to Minor League camp.
Mastny spent all of last season with the Tribe, going 7-2 with a 4.68 ERA in 51 appearances. He had an outstanding outing against the Red Sox in Game 2 of the American League Championship Series, shutting down the heart of the Sox lineup in the 10th inning of a game the Indians went on to win.
The 27-year-old Mastny came into camp with the upper hand in the bullpen battle but lost it by putting up a 6.39 ERA in nine exhibition outings, and fell behind veteran right-hander Jorge Julio in the pecking order.
"He's done a good job and served multiple roles for us," manager Eric Wedge said of Mastny. "We just don't have a spot for him."
The Indians gave a spot to Julio, who spent last season with the Marlins and Rockies, after he put up a 1.64 ERA in nine spring appearances.
"Everybody knows he has a great arm," Wedge said of Julio, "but we saw him pitch with some consistency. He worked himself into some situations, but then he pitched himself right out of it."
Breslow, 27, was thrust into an enviable situation. After getting caught up in a numbers crunch with the Red Sox, he was picked up off outright waivers by the Indians, who will use him to replace the deposed Aaron Fultz as the second left-hander in the bullpen.
"It was good for us to see him," Wedge said. "He's a young pitcher with some upside and the ability to help us."
Though Wedge hasn't officially announced it, third baseman Andy Marte, who is out of Minor League options, will be on the Opening Day roster as a backup to Casey Blake.
Marte has made six errors in the field this spring and batted just .204 at the plate.
"Andy is capable of being a good third baseman," Wedge said. "There are things he can continue to work on to be able to play over there when we need him to play over there."
Wedge said the final roster moves will probably be made Thursday morning. The Indians will break out of Florida camp after Thursday's home game against the Rays and head north to Atlanta for a pair of exhibitions against the Braves. The season opener against the White Sox is at 3:05 p.m. ET Monday at Progressive Field.