Saban said on his radio show Thursday night that Mosley was probably out with an elbow injury, then confirmed Friday night that the 6-foot-2, 234 pound sophomore would not play.
Mosley, who injured his elbow in the Tide's 38-14 win over Arkansas, returned an interception for a touchdown against Florida last season.
Saban said Mosley was "ideally suited" for this matchup because of his speed.
Saban said junior Nico Johnson will fill Mosley's role.
Pat Forde is a senior writer for ESPN.com. He can be reached at ESPN4D@aol.com.