The 28-year old Australian injured his ankle at the end of training on Friday which forced him out of the 3-1 loss to Everton at Goodison Park on the weekend.
The Royals, who currently sit second bottom on the table, will now prepare for the trip to third-bottom Aston Villa this Saturday and manager Brian McDermott hopes Federici is back in action as the Berkshire look to stave off relegation.
"Adam picked up his injury in training on Friday, which was unfortunate," he said.
"We were about to wrap up the session - he was in a lot of pain. We don't know how bad it is. It's not fractured, it's swollen a little bit so we'll see how it's going to be for next week."