John Carlson returned to Minnesota two years ago, signing a lucrative contract to join the Vikings as a tight end.

The contract was restructured last year after Carlson had only eight receptions in 2012, and the Vikings sought to restructure it again last month after a concussion ended his 32-catch 2013 season.

The sides could not reach a deal, and Carlson will be released Wednesday, two NFL sources confirmed.

The Litchfield, Minn., native signed a five-year deal worth $25 million in 2012, with $9 million guaranteed. Carlson’s restructured contract last season did not involve the final three years of his deal, and he was scheduled to make $5 million next season.

The Vikings can spread the cap savings over the next two seasons if they release Carlson with a post-June 1 designation, or they could add the savings to their cap space for 2014. The Vikings enter free agency this weekend an estimated $32 million under the salary cap.

Carlson played 27 games and had 40 catches for 387 yards and one touchdown over two seasons with the Vikings. He finished last season on injured reserve because of a concussion he suffered in Week 14 against the Ravens. It was his third reported concussion in six NFL seasons. Carlson reviewed his health in the offseason with his family, and plans to continue his football career next season.

“It’s a serious thing, but I’m not ready to be done,” Carson said in February. “I’m not done, and the doctors are telling me that it’s OK that I’m not done.”

Most of Carlson’s production last season came in a five-week span when he started after Kyle Rudolph broke a foot in Week 9.

“It was frustrating to end the season on IR because things just started to go well for me there kind of midway through when I had a chance to do a few things,” Carlson said. “I was having a lot of fun and that’s disappointing. This is football. It’s a physical game and concussions happen.”