No Progress For Celtics' Al Horford

BOSTON (CBS) -- The Boston Celtics were hoping to have Al Horford back in time for Wednesday night's game against the Wizards, but his status is again in doubt as the big man has not progressed in the NBA's concussion protocol.

Horford suffered the concussion last Monday during practice and has missed Boston's last three games. Celtics head coach Brad Stevens said Monday that Horford has yet to resume basketball activities.

"[Horford] has not advanced in the protocol, based on what I've been told," Stevens said following practice, according to ESPN's Chris Forsberg. "I have not gotten anything deeper than that, but he did not do anything with our team today."

The Celtics are set to leave for Washington D.C. on Tuesday, and it looks unlikely that Horford will make that trip. He did some light on-court activities over the weekend, under the watchful eye of trainer Ed Lacerte, but he's yet to increase his workload, a pivotal step in his return. A player must be symptom-free to advance in the league's protocol, and receive clearance from the league and team doctors before returning.

Horford averaged 12 points and five rebounds in his first three games as a member of the Celtics, and the team has sorely missed him on the defensive end during his three-game absence. Tyler Zeller has started in Horford's place and averaged 9.3 points and 6.3 rebounds over 26 minutes per game, with Boston going 1-2 in Horford's absence.