CINCINNATI -- The Cincinnati Bengals announced Tuesday that they have kept quarterback Zac Robinson on the physically unable to perform list and waived fullback Chris Pressley as a three-week window to activate them to the 53-man roster expired.

Per NFL rules, teams have a 21-day window in which they can allow players on the PUP list to practice and participate in normal team activities. If after that 21 days team don't activate them to the playing roster, they have to waive them. Since Pressley practiced the last three weeks after having cleared a physical, he was eligible to be added to the roster. The Bengals, however, decided not to make that move.

In Robinson's case, since the team never cleared him to practice within those 21 days, the backup is able to remain part of the club but he must remain on the PUP list for the remainder of the season.

Both players suffered injuries that predated the start of training camp and were placed on the PUP list as a result. Robinson had an elbow injury and Pressley had a knee issue.

Since the Bengals haven't had a true fullback all season, it appeared Pressley had a chance to make the team if he returned to fully conditioned health. In an effort to work around his absence in the lineup, the Bengals moved Orson Charles from tight end to fullback in the preseason in an effort of grooming him into the role. Charles has barely played this year, though, and the Bengals have been more content with using rookie tight end Tyler Eifert in fullback situations, lining him up in the backfield as an H-back. When Eifert isn't run-blocking from there, the Bengals have mostly gone with a two-halfback formation that puts BenJarvus Green-Ellis and Giovani Bernard in the backfield at the same time.