The former Rangers attacking midfielder believes that Morelos is “special at times”, but he has pointed out that the striker does tend to let himself down.
Miller has suggested if a club makes an offer of £15 million or £20 million in the summer transfer window, then Rangers should sell him.
Miller told The Daily Record: “If you can get £15m or £20m for Morelos, you are taking it, aren’t you? Especially as there seems to be some interest in other strikers at the moment.
“Morelos is special at times and lets himself down at others. You look and think he’s learned and then something happens.
“If he’d have stayed up against Celtic and scored in December, he’d have been flying coming back, but he returned not looking himself.”
Morelos is a player in demand, with a number of clubs reported to be interested in securing the services of the Colombia international striker this summer.
The Scottish Sun reported in May that Leicester City, Newcastle United, Everton, West Ham United and Crystal Palace are interested in signing the 24-year-old in the summer transfer window.
FootMercato reported this month that French club Rennes are looking to make a move for the striker.
Rangers stay or exit?
Morelos is the first-choice striker at Rangers and is the main goalscorer at the Gers.
If Rangers do decide to sell the 24-year-old, then they have to make sure that they sign a suitable replacement.