I know less than I did before I read this 

Posted 9:50 AM by Sean
According to Mike Scarr on the Angels' website:

If Colon cannot go Saturday in a potential Cy Young battle with Jon Garland,
left-hander Joe Saunders will likely get the nod. The rookie was called up Aug.
16 and made a spot start against the Blue Jays. Over 7 2/3 innings, Saunders
allowed two runs on five hits and two walks.

I'm not sure why Scarr says this, since he doesn't back it up with anything from anyone in a position to know who's likely to start on Saturday. He quotes Scioscia as saying that if Saunders starts, he'll surely do a good job, but that's neither here nor there. Escobar did warm up briefly in the bullpen last night, but was not used in the game.

In the same article, we learn that Maicer Izturis, while not back at full strength, should now be available as a late-inning defensive replacement.

Update: Things get clearer on the Escobar/Saunders situation. DiGiovanna in the Times says:

If ace Bartolo Colon (pain in lower back) can't make Saturday's scheduled
start against the White Sox, rookie left-hander Joe Saunders — and not Kelvim
Escobar — will probably pitch.

Escobar, who could emerge as one of the Angels' primary set-up men, warmed
up in the eighth inning Thursday night, and Manager Mike Scioscia said he would
be available in relief tonight.

"He could be a valuable piece to the bullpen, and you'd hate to bypass that
for an opportunity to start Saturday," Scioscia said of Escobar.

MLB.com's probable pitchers page agrees:

Colon is tentatively scheduled to start against the White Sox. The right-hander
left in the sixth inning of his last start with soreness in his lower back. If
Colon does not start, rookie left-hander Joe Saunders will get the call.
Saunders is 0-0 with a 2.45 ERA in one start with the Angels this season.

I still think they should wait and see what happens tonight before making the call, though.