Rangers will feature in the Scottish Premiership during the 2016-17 campaign after winning the Scottish Championship title with ease this past season.
The Gers have already recruited former Newcastle United and Queens Park Rangers midfielder Joey Barton on a free transfer this summer.
Jordan Rossiter, Matt Crooks and Josh Windass have also been signed by Glasgow giants Rangers.
Former Rangers attacking midfielder Miller believes that the Gers need to bring in five or six new players in order to compete with Old Firm rivals Celtic next season.
The Scotsman has also predicted that Celtic will make at least one big signing in the summer transfer window.
“Looking at the squad, I feel Rangers need another five or six players to go and mount a challenge,” Miller told The Scottish Sun. “A lot will depend on what Celtic do but I’d expect them to make at least one big signing.
“Brendan Rodgers will probably want another striker to play next to Leigh Griffiths and I could see him making a marquee buy.
“If that happens, and Celtic spend a bit of cash, then Rangers will need to go out and add a bit more quality.”
Rangers have a good squad, but they do need to make more additions in order to have a successful 2016-17 campaign.
The Gers will be expected by many to challenge for the Scottish Premiership title next season.
Celtic will start the campaign as favourites for the title, but Mark Warburton’s side will be determined to give them a run for their money.