The Braves rookie outfielder has a bone spur in his right ankle, cutting down his speed a little bit.
"I've had it the last two months, but it's getting worse," Blanco said Monday.
Atlanta manager Bobby Cox sat the left-handed-hitting Blanco for the series finale against San Francisco, which might have happened anyway with left-hander Barry Zito pitching for the Giants.
That doesn't mean, however, that Cox isn't concerned about Blanco's ankle.
"It's sore," Cox said. "It's an issue."
Speed is a big part of Blanco's game. He went into Monday tied for fifth in the National League with 24 infield hits. That's tied for the sixth-highest season total for the Braves since 1988, when the stat was first tracked.
The 24-year-old has become the Braves' main leadoff man and his 11 steals are the most on the team. His average is just .258, but he has a .371 on-base percentage thanks to 62 walks.
Before this year, Blanco was considered to be too much of a free swinger -- delaying his arrival in the Major Leagues.
"Pretty good," Cox said when asked about Blanco's adjustment to the leadoff spot.
The native of Venezuela is also valuable because of his ability to play all three outfield spots. He twice threw out baserunners from left field in the series opener against the Giants.
"He's played good," Cox said. "I want him out there."
After spending seven years in the Minors before getting his chance, Blanco is determined not to let a sore ankle hold him back.
"I want to keep playing," he said. "This has been a good year. I want to keep it going."
Guy Curtright is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.