Beckett was supposed to pitch the bottom of the second inning, but he informed American League manager Ron Washington that his knee, which he hyperextended Friday, was sore.
"I was almost done with my warmups. I think I had about 10 pitches left," Beckett said. "A lot of it is you don't get to go through the same routine. You're rushing around, you're doing this, you're doing that. It's in the back of your head when you feel it. You're like, 'If something happens here, I'm going to make a lot people out here look not good, including myself.'"
However, Beckett emphasized that the ailment remains minor and nothing that should prevent him from making his next start on Sunday night at Tropicana Field against the Rays.
"I don't think so," said Beckett. "I could have pitched. I'm not comfortable going out there and getting hurt in the All-Star Game and costing myself starts in the second half. I think that's how everybody should be. This game does mean a lot with the home-field advantage and everything, but at the same time, there are some important things that are ahead."
Washington didn't use Beckett's absence an excuse for the AL's 5-1 loss.
"Well, you know, we had to make an adjustment, and that's exactly what the game is about," said Washington. "But we were able to get some pitching out there, so we are not going to use not having Josh as an excuse."
If it had been a regular-season start, Beckett suspects he could have pitched.
"I think I would have pitched through it," Beckett said. "It wasn't one pitch, it just kind of progressively got a little bit stiffer. I don't know what to say. It [stinks] to be warming up in an All-Star Game and have that happen. I was in a good situation, I was pitching early in the game, I was going to be able to hang out with the guys for the last few innings. It's tough, but I think I did the right thing here."
Washington told all the players on the AL squad he wanted to return them to their teams in the same shape they arrived.
"I'm sure he understands," Beckett said.
Of course, Beckett had also been in touch with Boston manager Terry Francona in the days leading up to the game.
"I told Tito when I left [that] if I feel [it] at all when I'm out here I'll speak up, and it just wasn't something I was comfortable going out there and messing with," Beckett said. "I don't think I reinjured it, but I've definitely still got some inflammation in there."
Prior to the game, Beckett was looking forward to being able to pitch for the AL.
"It's cool," Beckett said of pitching in All-Star Games. "It's different though. You know what I mean? I don't know why. I can't really pinpoint the one thing that makes it different, but it doesn't feel the same. It doesn't feel like a playoff deal or anything like that. It's just different. I can't really put my finger on it."
In 17 starts this season, Beckett is 8-3 with a 2.27 ERA.
The Red Sox already have three starting pitchers on the 15-day disabled list -- Jon Lester, Clay Buchholz and Daisuke Matsuzaka, the latter of whom is out for the season.
This was Beckett's third All-Star appearance. He got the win in 2007, firing two shutout innings in San Francisco. Beckett didn't pitch in '09 at St. Louis, and in a late surprise, was again reduced to spectator status in this one.
Yankees right-hander David Robertson pitched the second instead of Beckett.