The 31-year-old struggled for form last season as he entered the year coming off an ACL tear, and was not as sharp in his route running for the Steelers.
However, Haley feels that in his second year back from the injury, Miller will look like his old self.
"Heath is night and day from where he was last year at this time," Haley told reporters.
"He wasn't even ready to go that first game, and it took awhile to get back to where he was close feeling 100%. He's 100% ready to go. I'm excited to about him being out there for us."
The Steelers face the Cleveland Browns in their season opener tomorrow.