Warburton was appointed the Rangers manager in the summer of 2015 and has a contract until June 2018.
The former Brentford boss has done a remarkable job at Ibrox so far and has guided the Gers back to the Scottish top flight.
Rangers won the Scottish Championship title this past season with ease and gained automatic promotion to the Scottish Premiership for the 2016-17 campaign.
The Gers also clinched the Scottish Challenge Cup and reached the final of the Scottish Cup.
Rangers managing director Stewart Robertson recently told The Daily Mail that the club are in talks with boss Warburton and assistant manager David Weir over a new deal.
Former Rangers star Johnstone has suggested that handing Warburton a new contract means that next summer clubs would have to pay in order to take him away from Ibrox.
“If Rangers continue to do well next term, Mark will be a manager that a lot of clubs look at,” Johnstone wrote in The Glasgow Evening Times. “You don’t get linked with positions when you are performing poorly or you are not doing a good job.
“He will be looked at and it could prove difficult to hold onto him so Rangers are looking after themselves a bit as well here. If someone does come in, they will have to pay for Mark.
“If there comes a point when he does move on, then Rangers have to make sure that they get a good deal for the club.”
Former Rangers midfielder Barry Ferguson has backed the Scottish club’s decision to reward Warburton with a new deal.
“It looks like a good bit of business because it tells the manager that all of his work has been recognised and rewarded and that he is not being taken for granted,” Ferguson wrote in The Daily Record.
“It’s not so much about how much cash he can squeeze out of the club, it’s about moving forward as a united front. That’s the message Rangers will send out when this contract has been signed and sealed.”
Rangers will be aiming to compete with Old Firm rivals Celtic for the Scottish Premiership title next season.