New England Patriots quarterback Tom Brady left the field on Wednesday with a knee injury.  While it could be nothing serious, the injury did occur to Brady's left knee - the same knee that sidelined him during the 2008 season with an ACL tear.  If the injury is serious, New England would have exactly what they didn't think possible - a quarterback controversy involving Tim Tebow.

Brady left practice Wednesday afternoon with an injured knee.  He went down during 11-on-11s and left, only to come back in the following play.  It didn't last long and Brady soon left the field with a trainer after consulting coach Bill Belichick, according to multiple news outlets (via Pro Football Talk).

The seriousness of Brady's injury is uncertain.  It could be nothing, but it did happen on his surgically-reconstructed left knee.  If it is a season-ending injury, which there is no indication of, it could lead to a competition between incumbent backup Ryan Mallett and third-stringer Tebow.

Although Tebow's preseason performance last week makes the idea of Tebow starting laughable, it could happen - Mallett is unproven.  The 2-year backup completed one pass in four games played last season, and this past week he went 9-of-18 for 97 yards. 

New England's offense is catered around Brady, who Mallett, a pocket passer, is comparable to.  But, based on last week's preseason game, the Patriots are developing packages geared toward Tebow's strength as a mobile quarterback.

Belichick admitted as much on Tuesday during his weekly radio appearance on WEEI (via ESPN): "...You want to try to be prepared for, and take advantage of, some of the players' skills that you have."

The notoriously tight-lipped Belichick also called Tebow the team's first running quarterback since Matt Cassel left in 2008.

There's a lot of ifs.  The first is if Brady's injury is even serious.  The next is if Mallett struggles leading the Patriots' offense.  The third is if Tebow is better than Mallett.  All of those ifs coming together, however, could spell what nobody ever thought could happen in New England: Tebow starting.