Infielder Joaquin Arias was activated from the disabled list in Cruz's place after successfully completing a rehab stint at Double-A Frisco.
Cruz suffered the injury during Saturday's 3-1 loss to the Red Sox and was forced to leave the game. On Monday, Cruz said before the start of the Rangers' three-game series against the Rays that he was surprised that he was placed on the DL but understood the decision.
"I don't feel any pain, even when I was running on the treadmill yesterday, but I guess the X-rays showed something different, some inflammation or something," Cruz said on Monday. "I get the point why they want me to go [on the DL]. They want me to be full strength for September, so yeah, I understand."
This is the third time this season that a hamstring issue has hampered Cruz, as a right hamstring issue shelved him in April and May, and a left hamstring strain sidelined the outfielder through most of June.
"It's hard to figure out why," Cruz said. "I have to figure out what kind of program I have to do in the offseason so it doesn't happen again."
When he's been in the lineup, Cruz has been a force for the Rangers, batting .320 with 16 homers and 64 RBIs. Now the team can only hope that one last trip to the disabled list can get Cruz's hamstrings healthy for the stretch run and the playoffs.
"Once again, we're talking about a hamstring," Rangers manager Ron Washington said. "We want to make sure it doesn't get any worse. He's such a valuable asset, we've got to watch it. We want to make sure it isn't anything more than what it is."
Washington said if it was mid or late September, the team would have kept Cruz active "as a pinch-hitter to help out," but nothing more, because there is the potential of worsening the injury.
Cruz described the injury as having the least effect compared to the other two this season and that he would "definitely be able to play" if it was late September.
"It's frustrating, of course, but I understand the point," Cruz said.
In his replacement, Washington will use Mitch Moreland, David Murphy, Vladimir Guerrero and the recently recalled Brandon Boggs. Murphy has made 32 starts in right field this season, with Guerrero making 10 and Moreland one.
Chris Girandola is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.