The USA international, 24, has been out of action since September due to a foot problem.
However, Williams is now in contention to return to the Royals squad for Saturday's Championship encounter at home to Queens Park Rangers.
"It felt really good to be back," he told the club's official website. "This is the kind of injury that takes a long time to heal completely but I feel like I'm back now. I feel like I'm ready to go.
"I have to see how the sessions go this week, that I don't have too much pain. It's the gaffer's decision but I'll tell him I'm ready and he can trust that I will put everything in."
Reading are currently in fifth place in the Championship table.