Simply put, they weren't going to get enough playing time going forward to further their development before the season opens. They were in camp primarily to help catch the many pitchers in camp during early workouts before games began.
"This is much better for working purposes," manager Jim Leyland said.
Both will have Tuesday off before reporting to Minor League camp on Wednesday.
McCann was the Tigers' top pick in the 2011 First-Year Player Draft out of the University of Arkansas. The 22-year-old split last season between Class A Lakeland and Double-A Erie, combining for a .237 average with 22 doubles, two home runs and 39 RBIs. He's expected to return to Erie for this season.
The 24-year-old Casali, a 10th-round pick in that same 2011 Draft out of Vanderbilt, split last season between West Michigan and Lakeland. Between the two levels, he hit .270 with 25 doubles, nine home runs and 43 RBIs in 94 games. Most likely, he'll return to Lakeland.