The 31-year-old is arguably the biggest signing of the eight players who have joined Rangers this summer, having played for Tottenham Hotspur in the Champions League and won 81 caps for his country Croatia down the years.
He joined the Gers after enjoying a stint with New York Cosmos in the United States and big things are expected from the playmaker, despite his advancing years.
Kranjcar and his new Rangers team-mates are still in South Carolina on a pre-season training camp, and Miller says that the Croat is already looking class in training.
"Niko's been getting bedded into training the last few days and he looks very, very good," he told Rangers TV. "He looks very comfortable [on the ball] which everybody knew he was and he's only going to get better and stronger."
Jordan Rossiter and Joey Barton are yet to join up with the club, while Matt Crooks is also missing in training through injury.
But Josh Windass, who joined Rangers from Accrington Stanley with Crooks, scored on his debut this morning as Mark Warburton's side edged out local side Charleston Battery 2-1, with Harry Forrester also on the scoresheet.