The official Twitter account for the Lions announced the knee injury for Bush, stating that his return was questionable.
Chris Wesseling from NFL.com tweeted out that Bush appeared fine on the sideline and was expected to return.
Bush returned shortly after, but that didn't last long. Dave Birkett from the Detroit Free Press reported that Bush was back on the sideline and things didn't look good.
This isn't the only injury that Bush has dealt with this season, and it's only the second game.
Bush injured both his left thumb and groin in the win over the Minnesota Vikings in Week 1. He finished the day with over 190 total yards and showed his toughness, which you can see here as the training staff helped pop his thumb back in.
Despite his toughness, all of these injuries have to be concerning through two weeks. It's quite clear that he's already become an integral part of the Lions offense, and losing him for any amount of time would be a big blow.
Bush dealt with a number of injuries during his five years with the New Orleans Saints, missing 20 games from 2006 to 2010. He stayed healthy over the past two seasons with the Miami Dolphins, however, missing just one game.
To make things worse for the Lions, any missed time for Bush would expose a serious lack of depth at the running back position.
Joique Bell has looked good as a red-zone threat so far this season and did a good job in 2012, averaging 5.0 yards per carry, but he's never had a full workload.
The other option would be Mikel Leshoure, who averaged just 3.7 yards per carry last season.
Losing Bush would also likely mean more throws for Matthew Stafford, which isn't a good thing. Stafford threw the ball an NFL-record 727 times last season, shattering the previous record of 691 and making the Lions offense extremely predictable. The Lions need Bush to keep the offense more balanced and effective.
This was a very promising year for Bush, but if this knee injury is serious, it would be a serious blow for the Lions.