Hamels said he woke up Wednesday with a stiff neck and it kept getting worse. He could barely sit on the Rangers' plane ride from Seattle to Chicago.
"Sometimes in hotels it happens, I guess," he said. "Everything comes down to timing. If this happened the day after we could get through it and get to the next game. Something that happens right before your start, there's not enough time to be able to get right and go out there and give your team six, seven innings and a hundred pitches without something really disastrous happening."
Veteran right-hander Doug Fister moved up one day to pitch the series opener against the White Sox on regular rest. He tossed seven scoreless innings in the Rangers' 4-2 loss.
Now Matt Moore will move up one day to pitch on regular rest Friday. The Rangers were off on Monday.
Hamels, 34, is 2-4 with a 3.48 ERA in nine starts this season. He pitched six sparkling innings in a 1-0 victory against the Astros last Friday.
"At times we do pitch through some bumps and bruises, and I did think about how far I could push it," he said. "But when you notice you cannot look at a target when you throw a baseball, it's not good."