The visitors, meanwhile, head into this fixture looking for a third consecutive win to solidify their place in the playoffs.
Match preview
Los Angeles Galaxy rose to the top of the Western Conference after a hard-fought 3-2 victory over Colorado Rapids at Dignity Health Sports Park on Wednesday.
Greg Vanney's men have alternated between wins and defeats in the last four games, an inconsistency that follows an impressive four-match winning run from mid to late June, which has prevented them from opening up a significant gap at the summit of the table.
Nonetheless, Los Angeles are still two points clear at the top of the Western Conference table, but they will be hoping to hold onto the spot by winning two games in a row for the first time since June.
To achieve successive victories, the Galaxy will need to end an ongoing four-match winless run against their Sunday opponents, losing three times and drawing once across all competitions, although the loss came in a friendly.
Barring the defeat to Los Angeles FC on July 5, Vanney's side have been excellent at home, picking up the second-most points on home soil among teams in the Western Conference.
Since late May, Portland Timbers have found their form, with their only blemish since then being a rare defeat to Dallas on July 5.
Phil Neville's side have now scored seven goals since that defeat, first dispatching Nashville SC 4-1 before putting in an impressive performance last Saturday, thrashing one of the league's top sides, Real Salt Lake, 3-0.
The Timbers are in seventh place in the Western Conference table, with 36 points from 24 matches played, two points adrift of the top four.
The visitors currently occupy the final guaranteed playoff spot, but they are just two points ahead of eighth-placed Houston Dynamo, and any slip-up could potentially see them surrender this position.
Los Angeles Galaxy Major League Soccer form:
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Portland Timbers Major League Soccer form:
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Team News
Los Angeles Galaxy will remain without leading scorer Dejan Joveljic who is still nursing a hamstring problem that has kept him out.
Julian Aude also misses out for the hosts through a groin injury, while Gaston Brugman is yet to fully recuperate from a damaged knee.
Gabriel Pec has directly contributed to 18 goals, the most by any LA Galaxy player, and he is the man to watch on Sunday.
Portland Timbers will take to the pitch once again without right winger Marvin Loria, who has been out since February with a knee issue.
Evander, who has 21 goal contributions - the most by any Portland player - will be looking to directly contribute to a goal for a sixth consecutive match.
Los Angeles Galaxy possible starting lineup:
McCarthy; Cuevas, Yoshida, Neal, Yamane; Cerrillo, Delgado; Fagundez, Puig, Pec; Paintsil
Portland Timbers possible starting lineup:
Pantemis; Mosquera, Araujo, Zuparic, Bravo; Chara, Williamson; Moreno, Evander, Rodriguez; Mora