Receiver Austin Collie is working out Thursday for the San Francisco 49ers, a league source told ESPN NFL Insider Adam Schefter.

Collie worked out earlier this week for the New England Patriots, a source told ESPNBoston.com's Mike Reiss.

Collie is working his way back from a knee injury that cost him all but a game last season with the Indianapolis Colts. He also has suffered three serious concussions in his career and recently told USA Today Sports that he would sign a waiver if required in order to play.

"I'll sign a waiver, all right?" he told USA Today. "They're not going to have to worry about me suing. I'll hold myself to be accountable ..."

"I just need that closure. When I feel like I accomplish everything I want to accomplish, I'll have no problem walking away from the game. But I have more to give."

Collie has 173 career receptions in 42 regular-season games (16 starts), totaling 1,845 yards and 16 touchdowns.

The 49ers have a need at the receiver spot due to the Achilles' tendon injury suffered by Michael Crabtree that might sideline him for most of the season.

The 49ers' depth chart at receiver is led by veteran Anquan Boldin and 2012 first-round pick A.J. Jenkins, who didn't have a catch last season but is impressing coaches this offseason. Other receivers on the team include veteran Mario Manningham and rookie Quinton Patton.

Information from ESPN NFL Insider Adam Schefter, ESPNBoston.com's Mike Reiss and ESPN.com's Paul Kuharsky was used in this report.