EUGENE -- Oregon has lost a key member of its starting offensive line, likely for the remainder of the regular season.

Freshman left tackle Penei Sewell, who suffered a right ankle injury during the Ducks' 30-27 overtime win over Washington on Saturday, is out for "approximately six weeks," the program announced Tuesday morning.

Oregon coach Mario Cristobal isn't sure whether Sewell, who started the first six games at left tackle for the Ducks, will be out for the rest of the regular season or be able to return sooner than a bowl game.

"It's hard to tell," Cristobal said. "He's got to heal up and healing injuries versus rehabbing a guy back are so different because everyone heals differently. He is a little bit of kind of a freak of nature in terms of the way his body develops. Hopefully he'll heal sooner than later, but it's going to be about player safety first and player welfare first. I feel terrible for him because I think you see him, the way he practices and competes, this is his passion. I know he'll miss it a ton but at the same time he'll be a factor in the O-line room just serving as an extra coach."

Oregon described it as a "high ankle injury" and reading between the lines of how Cristobal described Sewell's injury it sounds more like a sprain than a break, but he declined to specify.

Left guard Shane Lemieux described it as a "tweak," which would be more in line with a sprain.

When Sewell went down, the Ducks moved right tackle Calvin Throckmorton to left tackle and inserted backup Brady Aiello at right tackle. Throckmorton and Aiello were the first-team tackles during Tuesday's practice.

"You never want to see one of our fellow teammates go down," said Aiello, who has come in to replace injured starters back-to-back years. "It's kind of the worst feeling you can possibly get as a teammate, seeing your guy go down. Got to stay ready for when that time comes because it's not guaranteed for anyone. One play can be your last play. That definitely showed and can't take it for granted."

Pro Football Focus ranks Sewell, the first Oregon true freshman to start on the offensive line in a season opener since 1997, as the No. 6 tackle in the nation.

"That guy really has done a great job helping us establish a certain demeanor up front," Cristobal said. "He also understands that this is sometimes the nature of the game, is that it is unforgiving and that during this time there could also be a lot of improvement in terms of the way he analyzes film, studies opponents, studies himself.

"He has six games and 100 practices to study on himself. He'll use his time wisely and he'll come back even more motivated than ever. I think in the end you'll even see a better Penei Sewell."

-- James Crepea | jcrepea@oregonian.com | @JamesCrepea