The team doctors felt they needed to open up his knee to get rid of the infection.
"The knee wasn't progressing like it should," Johnson said. "The orthopedic surgeon said they were going to have to open [the knee up] a little bit to get the infection out. So he will not be joining us on this trip [to New York."
Johnson found out about Brown's problems on Sunday, when the Nationals were packing their bags for a four-game series against the Mets that began Monday. The team doctors then suggested to Johnson that Brown would be better off if he didn't travel.
Since his promotion to the big leagues last Tuesday, Brown has been hitless in three at-bats for Washington.