The season opener is four months away and a lot can happen between now and then, but the Green Bay Packers are starting the off-season with some major changes on their offensive line.

The most noteworthy is that right tackle Bryan Bulaga is moving to the left side to be quarterback Aaron Rodgers' blind-side protector, replacing last year's starter Marshall Newhouse.

In addition, the coaches have flipped guards T.J. Lang and Josh Sitton, moving Lang from left to right and Sitton from right to left. Newhouse, 2012 undrafted free agent Don Barclay and 2011 first-round pick Derek Sherrod will all have a shot to start at right tackle.

Initially, multiple sources detailed the move, and later after an interview request, coach Mike McCarthy confirmed it and agreed to discuss it.

"I sat down with Bryan and Josh on Monday and I told them I wanted to make the move to where they're on the left side," McCarthy said. "Those two are our most accomplished and experienced players. I told them about the responsibilities and my expectations about playing the left side.

"Some of the things we'll want to get into schematically as we move forward. They were excited about it."

The moves were timed with the advancement of the off-season program into Phase II, which is the first opportunity for the players to begin working with position coaches on the field. McCarthy could have eased the players into new roles but this is a commitment to solidify the left side and protect a quarterback who just signed a five-year, $110 million contract extension.

Last year, McCarthy tried to make it work at left tackle without moving Bulaga, but Sherrod suffered a leg fracture from which he still hasn't returned and Newhouse was a big disappointment after showing some promise in '11.