Seager becomes the latest newcomer to a team that already has brought up rookie position players Dustin Ackley, Carlos Peguero, Greg Halman, Mike Carp and Mike Wilson this season, though Carp and Wilson have since returned to Tacoma.
"He's a line-drive hitter who sprays the ball all over the place," Zduriencik said. "He's a mature kid who understands the strike zone and has hit everywhere he's been. We're not expecting miracles, but he's a guy who deserves a shot."
Seager has split time between second and third base with the Rainiers, but will focus on third with Seattle since Ackley has established himself at second base since his own arrival three weeks ago.
Seager and Ackley were college teammates at North Carolina and were selected in the same Draft in 2009, with Ackley the second overall pick and Seager going in the third round.
Seager's arrival again changes the landscape for veteran Adam Kennedy, who moved from second to third after Ackley's call-up. Kennedy, 35, has been one of Seattle's most consistent hitters at .264 with six home runs and 28 RBIs and will continue to have a place in the lineup.
"Adam can play four positions: DH, first, second and third," Zduriencik said. "With young kids at two of those spots, he'll get time there and he can also rest [Justin] Smoak sometimes at first. Adam isn't a guy you run out there seven days a week at his age. But he's been wonderful and he'll be a big part of what we're going to be doing."
To make room on the 40-man roster, Seattle designated catcher Jose Yepez for assignment. Yepez, 30, spent a week with the Mariners, but never got into a game as he was called up as insurance for the injured Miguel Olivo and Chris Gimenez.
The move for Seager came shortly after Seattle dropped a 2-0 decision to the A's, managing just two hits as their record fell to 43-44 despite another strong pitching performance from Jason Vargas.
Seager will join the team on Thursday in Anaheim, where the Mariners open a four-game series against the Angels.
Before his promotion to Tacoma, Seager hit .312 with 25 doubles, four home runs and 37 RBIs in 66 games with Double-A Jackson.
Seager, a left-handed batter, hit .345 with Class A High Desert last year, racking up the most hits of any Minor League player in the country with 192 in 135 games.
His arrival would seem to indicate even less playing time for Chone Figgins, who has seen his role diminish since Ackley's addition. Figgins did play third base on Wednesday, with Kennedy at DH, but went 0-for-2 and committed an error as his batting average dropped to .183.