The undrafted Herzlich, 24, would be tasked with containing the NFL's second-leading rusher, LeSean McCoy, and backup quarterback Vince Young after a season of waiting to break into the starting defense.
"This is what I've been waiting all my life for, just a chance," Herzlich told The Associated Press on Friday. "The biggest thing to keep in mind is to just stay poised and play football. You just got to make plays, run to the ball, and tackle them."
"He's a big man and he's physical," Fewell said. "Mark's a go-getter. He's one of those 100 percent guys that if he sees something, he's going to go smack it and ask questions later."
The Associated Press contributed to this report.