SAN FRANCISCO -- Justin Smoak's tenure with the Giants is over after six hitless at-bats.

Smoak was designated for assignment to clear a spot on the 28-man roster for left fielder Alex Dickerson, who was reinstated from the paternity list on Monday. Dickerson took a two-game leave of absence over the weekend, as he and his wife, Jennifer, welcomed their first child, Levi Ross, on Sunday.

With outfielder Mike Yastrzemski still nursing a calf injury, Dickerson slotted back into the leadoff spot against right-hander Germán Márquez in Monday’s series opener against the Rockies at Oracle Park.

Smoak, 33, joined the Giants on a Minor League deal on Sept. 9 and subsequently replaced the popular Pablo Sandoval on the club’s active roster. The Giants believed Smoak could give them more left-handed power off the bench, particularly against righties, but they couldn’t afford to carry another player who profiled strictly as a designated hitter option following the injuries to Yastrzemski and Austin Slater, who hasn’t played the outfield since Aug. 11 due to an elbow issue.

“It just created a lack of positional flexibility for us,” manager Gabe Kapler said Monday. “When considering Daniel Robertson, by way of example, he can play several infield positions as well as the outfield. We viewed Smoak as a DH-only candidate, pinch-hit opportunities for us, so those are the reasons that we made this move.”

Kapler said it would have likely been hard to justify keeping Sandoval on the Giants’ roster for similar reasons. Sandoval, 34, caught on with the Braves last week and was assigned to their alternate training site.

“I think we'd be dealing with a very similar situation, understanding that we need players that can move around the diamond and that give us some defensive protection right now,” Kapler said.

Yastrzemski has begun to ease back into lower-body workouts and was slated to hit off a tee on Monday. He is still being held back from running, but the Giants have discussed the possibility of using him as a DH before he returns to the outfield.

“He's progressing nicely,” Kapler said. “I don't have an exact timetable for you.”

Worth noting

Jeff Samardzija (right shoulder impingement) was scheduled to pitch three innings at the alternate site in Sacramento on Monday. Kapler said the Giants view the 35-year-old veteran as a candidate to start one of the club’s doubleheader games against the Padres on Friday. Samardzija, who is in the final year of the five-year, $90 million contract he signed with the Giants in December 2015, logged a 9.88 ERA over three starts before landing on the IL on Aug. 8