"I give the kid a ton of credit, because it's not easy to come back," Riley said. "At the end of the day, this is where he wanted to be. We're thrilled to have him back. His teammates are thrilled to have him back."
Miller would have been a graduate transfer for the Fighting Illini but instead will spend his final season with the Sooners. Riley said Miller never enrolled at Illinois.
"A guy that can produce, a guy that's been a good special-teams player for us, as well, coming into a position for us that's got a lot of talent but is very thin," Riley said. "I'm thrilled he came back, no doubt. I'm glad it worked out."
Miller, who originally committed to Illinois out of high school before signing with Oklahoma, has caught 21 passes for 236 yards and four touchdowns over three seasons with the Sooners.
He isn't the only transfer wideout to spurn the Illini this offseason. After first committing there, Jeff Thomas also decided against transferring to Illinois and revealed he was heading back to Miami.
Information from The Associated Press was used in this report.