Jose Luis Real's side currently sit bottom of the Western standings, and defeat would see them become the second side, behind the hapless DC United in the East, to see their play-off hopes officially extinguished for this season.
Erick Torres' arrival on loan from parent club Chivas Guadalajara and Carlos Bocanegra's signing have sparked an upturn in the Los Angeles-based side's form, but it has likely come too late.
Torres has previously been linked with Manchester United and Tottenham in the Premier League and seven goals in just nine MLS outings, to put him top of the franchise's scoring charts, may well have caught the eye of potential suitors.
However, the Mexico Under-20 striker is not content with his fine form and is eyeing even better before the end of the season.
"I feel really good," he told Chivas' official website. "I still think there are some things I need to improve to reach my maximum.
"I'm working to reach that maximum and I think the team has helped me a lot to tally the goals that I have."
Chivas go into the game having lost just once in their last four, and they will be buoyed by the fact they have beaten Timbers the two times they have met at the Stubhub Center.
In the Eastern Conference, Montreal Impact, New York Red Bulls and Sporting Kansas City remain tied on 45 points at the top, although the latter are not in action this weekend.
Montreal host Columbus Crew and could be rattled by league top scorer Marco Di Vaio's claim that he could retire at the end of the season.
The former Italy international has struck 17 goals in 25 outings this term, but is keen on a return to his homeland, after his family's recent move back to Europe.
Meanwhile, Red Bulls will host Toronto, who are winless in six.
The top two in the Western Conference meet at CenturyLink Field as the Seattle Sounders host Real Salt Lake.
The Sounders have won their last four and will go top with a win over a Salt Lake side also in fine form, having secured seven points from their last nine available.
Colorado Rapids will hope to close the gap on Seattle, should they slip up, when they take on FC Dallas, themselves hoping to move back into a play-off spot.
Eastern play-off chasing Philadelphia Union and Houston Dynamo meet in Pennsylvania, fellow contenders Chicago Fire and New England Revolution clash at Toyota Park and San Jose Earthquakes will host the Vancouver Whitecaps, with both hoping to trouble those in the play-off spots above them.
LA Galaxy lost their first competitive game since July last time out against Colorado with internationals Landon Donovan and Robbie Keane missing, but will be confident of getting back to winning ways, despite a round trip of over 5,000 miles, when they take on DC United, who have won just three times all season.
