The San Francisco 49ers were handed their first loss of the season by the Seattle Seahawks on Monday night, and they also may have lost a key piece of their offense in the process.

According to Tom Pelissero of NFL Network, running back Matt Breida re-aggravated an ankle injury on Monday evening and will be seeking a second opinion. Pelissero notes that it doesn't seem like a severe injury, but it could be one that costs Breida some time.

With just seven games remaining in the regular season and the 49ers clinging to a half-game lead over the Seahawks in the NFC West, any time that Breida misses could obviously be crucial.

The third-year back has rushed for 542 yards and a touchdown while averaging five yards per carry this season. He struggled against Seattle, however, carrying the ball 10 times for just 18 yards.

Breida, who played his collegiate football at Georgia Southern, went undrafted but eventually landed with San Francisco in 2017. That season, he went on to play all 16 games, totaling 465 yards and a couple of scores while logging 4.4 yards per attempt.

Last year, the 24-year-old's role increased, as he registered 814 yards while reaching the end zone three times on the ground, posting 5.3 yards per tote. He also caught 27 passes for 261 yards and a pair of touchdowns.

The Niners have relied heavily on their rushing attack this season, so if Breida is sidelined for an extended period of time, it would certainly be a significant blow to Kyle Shanahan's club.

The 49ers will host the Arizona Cardinals next Sunday.