Thomas was outstanding in the Broncos Super Bowl XLVIII defeat to the Seattle Seahawks in February, as he set the Super Bowl record for receptions to no avail.
Most acknowledge Thomas as a top receiver in the NFL, but Decker went one step further and named the dominant wide-out amongst his top five best NFL players.
Decker himself is about to test the free agency market but he admits that Thomas is a class apart from himself.
"I think Demaryius Thomas is on a complete different level with his talent," Decker told the Denver Post.
"I think he's a top five-caliber receiver in this league. How it falls off from there, where you look at a receiver, I just try to be versatile and play all the positions. People might want to label me, but I don't want to put a label on myself."
The reason Decker could be on the verge of an exit from the Broncos is because the franchise deem him as a number two receiver that will be paid as a number one.
At this stage Denver don't want to make such a commitment and they are willing to take a chance and see what Decker can get from elsewhere.
"I respect (Jon Elway's) decision," Decker said. "Obviously, he has a philosophy in the way he does business. We'll see what it brings."