From ProFootballTalk.com: 

Bengals receiver Chad Johnson will undergo surgery to remove bone chips from his ankle, according to Adam Schefter of NFL Network.

Last week, agent Drew Rosenhaus pointed out that Johnson wasn’t practicing at a mandatory minicamp because of the injury.  Eventually, however, Johnson participated — possibly after being reminded that he had passed a physical and had been cleared to practice.

So the condition apparently isn’t something that prevents Johnson from playing.  Instead, it sounds like a matter of discomfort and/or pain tolerance. 

Johnson is expected to be ready for training camp.

He practiced last week and he should be ready for training camp. Still, the team has to be annoyed he didn't just get it done earlier in the offseason. It also gives Johnson an excuse if he wants to skip some practice. Johnson hasn't missed a game in seven years, so we won't be concerned unless it lingers well into August.