"I feel the same about Johnny as I always have," Shanahan told reporters Thursday. "Johnny is a playmaker. He's done that throughout his career. Nobody can argue with that at all."
Shanahan added that he believes Manziel will need time to adjust to the NFL game.
"Johnny is going to have some growing pains," Shanahan said. "He's played a type of football that he's not going to be able to down in and down out in the NFL, but you still want him to do it at times. He did it at times. You know he's going to have some bad plays from his lack of experience, and we hope to manage those and not put him in those situations as much."
Cleveland lost 30-0 to the Bengals in Manziel's first start, the team's first shutout since 2009.
Manziel completed 10 of 18 passes for 80 yards and was intercepted twice. Cleveland gained just 107 total yards, its fewest since 2004.
Manziel, the 22nd pick in this year's draft, won the Heisman Trophy as a college player at Texas A&M.
- Dan Gartland