Cooper joined Millwall, initially on loan in January 2017, and helped them win the League One playoffs and in the season after he impressed for the Lions.
He made 38 appearances in the Championship, not missing a game from December until the end of the season, and even contributed with four goals and three assists.
Rangers became interested in bringing the centre-back to Ibrox in the summer of 2018 and Cooper was convinced that a move to Glasgow was on the cards for him, especially with the money on offer.
However, Millwall stood their ground and refused to part ways with the centre-back and he has come to terms with the Lions’ decision.
Speaking to the South London Press, Cooper said: “I thought it was going to happen when you find out it is true and a conversation is going on.
“You think Millwall will say okay, because I’ve come in from Reading and I was only bought for around £250,000.
“So when the offer is in the millions, I thought it would be quick and easy.
“But Millwall made it clear that I wasn’t going and they wanted me to stay.
“I got onboard with that.”
Since the failed move to Rangers in the summer of 2018, Cooper has been a stalwart in the Millwall defence, making more than 40 league appearances in every season.
