Braves righthander Tommy Hanson missed a chunk of the 2011 season with right shoulder woes.

Two weeks ago, this report indicated that Hanson’s shoulder was “feeling good” and he was on target for a “regular routine” in spring training.

On Monday, Hanson was involved in a one-car accident in which he bumped his head. Tuesday, David O’Brien of the Atlanta Journal-Constitution tweeted:

#Braves Tommy Hanson will miss 2nd cons. day of workouts after banging head in a one-car accident Mon. morning.

— David O’Brien (@ajcbraves) February 21, 2012

And according to Fox-5 Atlanta, now we know why:

Tommy Hanson has mild concussion

— FOX5 Sports (@FOX5Sports) February 21, 2012

Mild or not, concussions are tricky things. Justin Morneau of the Twins had a collision at second base in the middle of the 2010 season that didn’t look like a problem at all, yet Morneau hasn’t been anything near the same player since.

You can bet that the Braves will take every precaution with Hanson, and even then, it can be difficult for players to return from concussions, no matter how “mild” they are.