"I was real sad [Friday] when I called my family because I never expected to be out this long," Ruiz said before Saturday's against the Arizona Diamondbacks at Citizens Bank Park. "It happens, so it could be worse."
Ruiz will be reevaluated in two weeks.
He became the 16th player who has appeared in a game for the Phillies to go on the disabled list.
"We've had a tough year," manager Charlie Manuel said, having to explain another key cog out of his lineup.
Ruiz said he started feeling pain when the Phillies played the Dodgers in Los Angeles during a three-game series from July 16-18.
"I tried to stay in the lineup because I wanted to play," he said. "I feel like it was worse every day."
Ruiz said he felt he was turning the corner following a 6-2 loss in Atlanta on July 29.
"I had a good day in the last game Sunday in Atlanta," he said. "I was feeling great and was happy."
That all changed when the Phillies traveled to Washington for a three-game series with the Nationals that began on Tuesday.
"When we got to D.C. it got me real good and I said it has to be something because no way you can feel OK one day and then the next feel pretty bad," he said.
Always known as one of the better defensive catchers, Ruiz has emerged during a breakout offensive season.
"It goes to show you how you can improve and what hard work can do for you," Manuel said. "He was an eight-hole hitter, a second cleanup hitter and now he is a first [cleanup hitter]."
Ruiz entered Saturday fourth in the N.L. in batting (.335), sixth in OPS (.959) and sixth in slugging percentage (.559). He also has a career-high 58 RBIs.
In order to qualify for any of the statistical titles, a player needs 502 plate appearances. Ruiz currently has 353.
The Phillies hold a $5 million club option on Ruiz for 2013 that is sure to be exercised. He will turn 34 in October.
This is Ruiz's fourth consecutive year being placed on the disabled list. The previous injuries were an oblique strain, a concussion and last season, back inflammation.
Ruiz hopes to return before the end of the season.
"I will do exercises and make sure I stay in good shape and be ready for September or whatever," Ruiz said. "I don't know how long it's going to be, hopefully less than a month."
Contact Marc Narducci at 856-779-3225, firstname.lastname@example.org or @sjnard on Twitter.