Seahawks head coach Pete Carroll told reporters Friday that Moore suffered the shoulder ailment during Thursday's practice. League sources told ESPN that the receiver isn't expected to require surgery.
"David hurt his shoulder, and he's going to be out for a bit," Carroll said. "We'll let you know more when I know more about it. ... He's going to be out a while."
The Seahawks already lost rookie wideout DK Metcalf, who recently underwent minor knee surgery. His Week 1 availability is in question after the procedure.
Seattle selected Moore in the seventh round of the 2017 NFL Draft out of East Central University. He emerged as a down-field threat last season, recording 26 catches for 445 yards and five touchdowns.
Moore is expected to play a pivotal role in the Seahawks' offense alongside Tyler Lockett, Jaron Brown and Metcalf. Keenan Reynolds, fourth-round pick Gary Jennings Jr., seventh-rounder John Ursua and undrafted rookie Jazz Ferguson are among the team's receivers fighting for spots on the 53-man roster.