Derek Johnstone has written in The Glasgow Evening Times that Rangers need to invest in the squad next summer.
The Rangers legend believes that the current squad is not good enough to compete in the Scottish Premiership.
“Rangers will be funded to the end of the season, and beyond, and we will see what money Mark Warburton is given to strengthen his squad during the January transfer window,” Johnstone wrote in The Glasgow Evening Times.
“Then, in the summer, there will need to be more cash invested in the squad for what we hope will be a Premiership campaign.
“This is a good squad but it won’t challenge once we get up another league.
“We need another handful of players that can come into the starting line-up and make an impact and that will mean money will have to be spent.”
Rangers are playing in the Scottish Championship at the moment and are on course to gaining automatic promotion to the Scottish Premiership at the end of the season.
The Gers are currently at the top of the league table with 33 points from 12 matches, five points clear of second-place Hibernian.
Manager Mark Warburton has the best squad in the Scottish Championship, but he will need to strengthen it next summer in order to compete in the Premiership.
Rangers, who lost to Hibernian away from home at Easter Road in the Championship last weekend, will take on Alloa Athletic at Ibrox in Glasgow on Saturday afternoon.
Anything other than a win for the Gers will come as a surprise.