Donovan is nursing a sore right ankle, an injury sustained last weekend during the Galaxy's 2-2 tie with D.C. United.
"His situation is to be determined, I would say at this point," Galaxy Coach Bruce Arena said of Donovan after the team practiced Thursday morning at StubHub Center.
Donovan was unavailable, but Arena said "he was out a little bit today" during the practice.
With six games left in the Galaxy's regular season, Seattle is in first place with 49 points in Major League Soccer's tight Western Conference.
The Galaxy is in fourth place but only five points behind the Sounders, so a Galaxy victory -- with its three points -- would lift the Galaxy to within two points of Seattle.
At the end of the regular season, the conference's top five teams advance to the MLS playoffs.