Rangers have drawn up a list of alternative centre-back signing targets should they fail to land Jake Cooper, according to the Scottish Sun.
Manager Steven Gerrard is keen on the Millwall defender and the club have tabled a £3million bid.
However, Millwall have indicated that they have no desire to sell Cooper or any of their first-team stars this summer.
Putting a contingency plan in place, Rangers have collated a shortlist of other defenders, including Blackpool stopper Curtis Tilt.
The 26-year-old would be available for a cheaper price of £1million after impressing for the ‘Pool in League One last season.
Tilt has just one year left on his current deal. Ipswich Town and Reading are also said to be chasing his signature.