Hamilton, who came out of Saturday's win over the Rays in the ninth inning, said the knee has bothered him for the last month and that he wanted something to alleviate the soreness.
He said he could pinch hit Sunday if needed, which he did by coming in for Craig Gentry in the bottom of the sixth. Hamilton hit an RBI single to left to cut the Rays' lead to 5-4. He then stayed in defensively, striking out in his second at-bat as the Rangers lost 9-5.
Manager Ron Washington expects Hamilton to be ready to start on Monday.
"It's nothing that's so painful that I can't play with it," Hamilton said. "But it's given out a little bit. It was a good time to get it taken care of."
Hamilton said he hasn't had any X-rays on the knee, but does not think it's anything structural. While he was in the minors, he had two surgeries on each knee to repair issues with his meniscus.
"It doesn't feel like that did," Hamilton said. "This is just inflammation."
Hamilton has fallen in the outfield while running after balls and said his knee has given out in those circumstances.
Hamilton, who turned 29 a few weeks ago, is hitting .299 with 11 homers and 32 RBIs. He hit a home run in each of the first two games of the Rangers' series with Tampa Bay, including a two-run homer on Saturday. He's second on the team in home runs and third in RBIs, batting in the No. 5 hole behind Vladimir Guerrero.
"Josh is turning the corner as far as how to gut things out, but at times we have to step in and help him," Washington said. "It's time we take care of it."
Entering Sunday, Hamilton was 10 for 22 in June, raising his batting average from .281.
Richard Durrett covers the Texas Rangers for ESPNDallas.com. Information from The Associated Press was used in this report.