tyler johnstone torn acl out for season. (USATSI)
Tyler Johnstone has been a three-year starter on Oregon's line. (USATSI)

The Oregon offense has suffered a major blow before the 2014 season has even begun.

Starting left tackle Tyler Johnstone is going to miss the entire season after tearing the ACL in his right knee. Johnstone confirmed the news to CSNNW.com, and also says that he'll undergo surgery on his knee Friday.

It's the second time Johnstone has suffered a torn ACL, as he tore the same ACL during Oregon's bowl win over Texas in December. He had been cleared by doctors to return after months of rehab on the knee, but Johnstone says he felt the same pop during the first week of Oregon's fall practice.

Johnstone has been a starter on the Oregon offensive line for three years. He's likely to be replaced by redshirt junior Andre Yruretagoyena, who has appeared in 11 games for the Ducks at both the guard and tackle position.