The Vikings will lose left tackle Matt Kalil to the Panthers when NFL free agency officially starts at 3 p.m. today, a source confirmed.

Kalil picked the Panthers in part to play with his older brother, Ryan, who is the longtime center in Carolina and turns 32 this month. The five-year, $55.5 million deal with $25 million guaranteed probably had a little something to do with that, too. USA Today has reported those terms.

The decision leaves the Vikings still grasping for at least one offensive tackle in free agency. Yesterday, Baltimore right tackle Rick Wagner reportedly agreed to join the Lions. This morning, Cincinnati left tackle Andrew Whitworth picked the Rams, per his agency.

Detroit's Riley Reiff, New York's Ryan Clady, Jacksonville's Kelvin Beachum and Carolina's Mike Remmers aren't yet spoken for as of this morning, but Kalil's deal may have opened the floodgates on the action at tackle.

LIVE TRACKER: Follow all of the Vikings' free agency moves

After making the Pro Bowl as a rookie, Kalil has not come close to consistently matching that level of play in large part due to injuries. While never missing a start in his first four seasons, knee injuries limited his effectiveness. Then a hip injury ended his season last September.

Vikings coaches felt that before the hip injury he suffered in August, Kalil was taking to the coaching of his new offensive line coach, Tony Sparano, and they were encouraged that he might regain his form.

Plus, Kalil was familiar with the team, the scheme and the area, which is why it made sense to try to keep him at the right price. But in the end, he is headed to Carolina, where the Vikings will travel this season.

ESPN first reported that Kalil has decided to sign with the Panthers.