The Galaxy (14-5-5) sit at the top with 47 points, while United (5-16-3) sits at the bottom with just 18.
But if there was ever a time for a trap game, this is it for the Galaxy, who are coming off a dominating 3-1 win over Eastern Conference leading Columbus last weekend to claim the league's top spot.
The big win put an end to a three game winless run and a streak of just one win and six, meaning the Galaxy haven't exactly been on top of their game lately.
"We have a harder time with teams down in the standings than teams at the top of the standings," L.A. coach Bruce Arena told the Galaxy website. "If we don't play well and hard for 90 minutes, we'll lose the game."
While United (5-16-30 has been struggling this season, they went into Toronto, where the Reds had lost just once in 12 matches in 2010, and earned a 1-0 victory against a desperate team. The loss stung the Canadian club so bad that it fired its GM and coach this week.
Julius James' 81st minute goal was the difference in the game.
"It was great, man," James told dcunited.com. "I was happy we were on the giving end of a late goal."
United will have to be prepared to deal with the hype of David Beckham on Saturday, with the English international expected to play just his second game of the season after returning last weekend from an Achilles tear. Beckham played the final 20 minutes vs. the Crew, and could see a couple more minutes vs. United.
"We're not building him from 20 minutes to 90 minutes," Arena said. "We're building him from 20 minutes to somewhere between 20 and 45, and then somewhere between 45 and 60. Once we're sure he can play 45 minutes, I think he's in position to start a game."
Listed as questionable for Saturday's game for the Galaxy are defenders Gregg Berhalter and A.J. DeLaGarza, and forward Edson Buddle, along with Beckham.
The United injury list is significantly bigger, with forwards Adam Cristman and Chris Pontius, midfielder Brandon Barklage, and defenders Marc Burch, Juan Manuel Pena, Barry Rice and Rodney Wallace all expected to miss the game. Also, midfielder Clyde Simms is listed as questionable.