Left tackle Matt Kalil underwent arthroscopic surgery on both knees this offseason, according to a report from USA Today. Kalil also received injections to help him deal with joint pain.

The 25-year-old had both his knees scoped in January by renowned orthopedist James Andrews, according to the report. In March, he underwent a procedure called Regenexx in which blood is removed, processed and re-injected into his knee. He also underwent platelet-rich plasma therapy.

It was the second straight offseason during which Kalil has undergone arthroscopic surgery.

Last spring, Kalil did not participate in team practices as he worked his way back after the surgery. He was ready by training camp, but he struggled, particularly in pass protection, during the season. He has said the knee troubles and missed practice time in the spring affected his confidence.

Kalil, the fourth overall pick in 2012, never missed a start in his first three seasons in the NFL.

He made the Pro Bowl as a rookie but has since regressed. And he had a much-publicized incident with a Vikings fan outside of TCF Bank Stadium after a loss to the Packers in late November.

The Vikings drafted two offensive tackles, T.J. Clemmings and Tyrus Thompson, during the final day of last weekend's NFL draft. But they also picked up Kalil's fifth-year option for 2016 on Monday.