But fatigue and tightness in the small of his back told him now is a good time to rest. So did videotape, which showed that he was throwing across his body and his sinker wasn't sinking.
Finally, head trainer Keith Dugger presented the closing argument to Cook (14-8, 3.87 ERA), who was convinced to delay his next start to the weekend or early next week.
The Rockies entered Tuesday's series opener eight games behind the first-place D-backs in the National League West and need this series. But the rest, he hopes, could mean he'll avoid the disabled list and an extended absence.
"He [Dugger] came up to me and was like, 'What do you feel about missing a start?'" Cook said. "He had to convince me a little bit. But in the long run, I knew that if I'd kept going out there, something worse could happen."
Cook has lost his last two starts, giving up 21 hits and 13 runs, 11 earned, in losses to the Nationals and the Padres. However, Cook has been less-than-sharp since the All-Star break, going 3-2 with a 5.13 ERA.
Cook's 172 innings are the second-most of his career, behind his 212 2/3 innings in 2006. But three innings not on the stat sheet might have had something to do with his current fatigue.
In his first All-Star Game appearance, Cook threw three scoreless but intense innings -- facing baserunners in a tie game -- on three days' rest.
"There's a lot of stuff, I think, could be part of it," Cook said. "Definitely, the All-Star Game could be a little bit why it happened.
"There's a lot of stuff that can contribute. But the fact is I've thrown a lot of innings, and this is the first wall I've hit."
Rockies manager Clint Hurdle, who managed the NL during the All-Star Game, said the fatigue factor for pitchers was one of the biggest concerns that hover over the All-Star Game, because home-field advantage for the World Series was on the line.
It was one of the issues that he discussed in a phone call with Major League Baseball officials in the days following the game. Hurdle said any extra-inning All-Star Game creates potential health risks for pitchers.
In addition to fatigue factors with pitchers such as the D-backs' Brandon Webb, who pitched two days before the game, the NL lost the Giants' Tim Lincecum to illness the day before the game.
"I clenched my teeth the entire time through the outing," Hurdle said. "As the manager of the team, you've got two-fold responsibility.
"One of them is to win the game, with the value that's put on it, the attention, the home-field advantage, and the second that I felt was just as important was to get everybody home safe."
Cook said the back "locked up on me" after the start against the Nationals, and it didn't feel better after the start against the Padres. Cook said he will throw his next side session on Thursday or Friday.
It's another odd injury for Cook, who missed much of 2004 and 2005 after life-threatening blood clots flared in both lungs.
A left oblique strain last season cost him the last two months of the regular season and the first two playoff rounds. He started the fourth and final game of the World Series, where the Red Sox swept the Rockies.
"Knock on wood, I haven't had any arm issues since I've been playing baseball," Cook said. "It's always been oblique or blood clots or something weird.
"I was talking to Dr. [Thomas J.] Noonan [the Rockies' medical director] about that, and he just said, 'Keep knocking on wood.'"
Thomas Harding is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.