METAIRIE, La. -- New Orleans Saints rookie offensive tackle Andrus Peat is expected to miss about four weeks with a sprained MCL, a source has confirmed.

The 13th pick in the draft injured his knee during the first quarter of Thursday's 31-21 victory over the Atlanta Falcons. The NFL Network first reported that Peat suffered a Grade 2 MCL sprain that will not require surgery.

Peat's injury comes after he made the second start of his career while filling in for injured starter Terron Armstead. The 6-foot-7, 316-pound Peat appears to have a bright future but remains a work in progress. He began this year as the Saints' top backup at both left and right tackle.

Armstead will likely return even sooner from his own knee injury after he was able to return to practice on a limited basis last week.

Armstead's return will provide a boost for a Saints offensive line that has struggled this year while battling a variety of injuries. The Saints managed one of their finest offensive performances of the season in the second half against Atlanta after an inconsistent first half.

The Saints were down to their third-string left tackle, Tony Hills -- a veteran journeyman who just signed with the team last week. Hills struggled early before settling in.

"I introduced myself to him last week: 'Hey Tony, I'm Drew, nice to meet you. And now you're starting for about 58 minutes of that game,'" Saints quarterback Drew Brees said. "He did a great job; he did an awesome job. A credit to him and his preparation ... he was ready for that moment.

"But it is kind of crazy to think you just signed a guy off the street a week ago and the next thing you know he's literally starting at left tackle for you."