Reed did not pass any of the concussion tests per NFL protocol this week.
Reed sustained the concussion in a 24-16 loss to the Philadelphia Eagles on Nov. 17. It robs the Redskins of one of their top offensive playmakers, as Reed has 45 receptions –- an NFL high for rookies -- for 499 yards and three touchdowns.
Reed's ability to beat man coverage and gain yards after the catch has helped the offense -- and will be missed against the 49ers. He's become a trusted target for quarterback Robert Griffin III because of his ability to not only get open, but to run the routes properly.
Losing Reed means veteran Fred Davis will return to the lineup for the first time since Oct. 13 against Dallas. Davis has been inactive in every game thereafter, costing him a chance at a $500,000 bonus for number of games in which he was active.
More importantly, the prolonged absence has cost Davis a chance to remind other teams that he can still play at a certain level. Davis will be a free agent after the season, and it's unlikely at this time that he'll remain in Washington. The Redskins re-signed Davis last offseason before drafting Reed in the third round.
Davis was the Redskins' best pass-catching tight end in 2011 and 2012, catching a combined 83 receptions and averaging 13.5 yards per catch in 19 games before rupturing his Achilles tendon.
Davis said the injury no longer bothers him, though he was slowed earlier this season by a sprained ankle. He has three receptions this season. Before his injuries, Davis was considered a good runner after the catch and had become a solid player for Washington. He had improved as a blocker as well.
But coaches also said Davis needed to work harder in practice. In the past, they did not have another option if Davis' approach was not to their liking. This year, the Redskins has an alternative in Reed, although coaches say Davis has responded.
"Fred just hasn't quit," Redskins offensive coordinator Kyle Shanahan said. "He's known that this year definitely hasn't gone for him how he wanted it to.
"We went with other guys in situations, and he's still come out. He's done a lot more scout team reps than he ever has done in his career. Some guys can mope and stuff on scout team, but Fred has worked harder on scout team than I've seen him work."
ESPN NFL Insider Adam Schefter contributed to this report.