Williams (elbow) will begin a rehab assignment with Single-A Fredericksburg on Sunday, Mark Zuckerman of NatsJournal.com reports.
Williams is finally ready to pitch in games again following last July's internal brace procedure on his right elbow. The veteran right-hander will likely need most, if not all, of the allotted 30 days a pitcher receives on a rehab assignment, but he should be ready to rejoin the Nationals' active roster sometime in July.