On Monday afternoon, the team placed Diaz on the 15-day disabled list with a left knee bone bruise. Filling Diaz's roster spot is Jordan Brown, who had his contract selected from Triple-A New Orleans.
Diaz has seen minimal playing time since being selected from New Orleans on May 2. In 10 games, the 35-year-old has appeared in 10 games and is 3-for-18 (.167).
He said he tweaked his knee while slipping on the basepaths in San Diego earlier in the month. In recent weeks, he has tried to play through the discomfort.
"The doctor said it's a bone bruise, and [Sunday] he finally said, we need to give it 10 days to relax," Diaz said. "We'd be trying our best with just the pinch-hitting and jogging slowly to first. Even that, it's just not responding."
Diaz had been wearing a brace of late.
Diaz was a right-handed bat off the bench option at left field. Now, the club has added another left-handed bat in Brown.
Brown, in the big leagues for the first time since 2010, has been used mostly at first base at New Orleans, and he's also played left field.
The 29-year-old previously had 26 games of Major League experience while with the Indians. In '10, he batted .230 in 87 at-bats with seven doubles and two RBIs.
The California native was a fourth-round pick of Cleveland in the 2005 First-Year Player Daft.
At New Orleans, Brown batted .261 with six doubles, one home run and 12 RBIs in 37 games.
With Diaz out, Miguel Olivo becomes a right-handed pinch-hit candidate on a bench featuring several lefties.
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter