That’s according to former Ibrox striker Kenny Miller after the Tynecastle Park club released a statement following the announcement the player had signed a pre-contract agreement to move to the Scottish league leaders in the summer.
It has been reported Rangers will attempt to sign Souttar before the transfer window closes at the end of the month but they were issued a warning by Hearts.
"The club reiterates that John is an important member of the first-team squad and will remain so until the end of the season unless a significant and satisfactory offer is made during the January transfer window,” a statement read.
Miller, who is now assistant boss at Falkirk, reckons Hearts will hold for half a million pounds.
"If you look at the fees that players have gone for in the past, it's big, big money," he told Clyde 1 Superscoreboard.
"Hearts, Hibs and teams in that kind of bracket, for their main assets, are normally netting two, three, four million, but you're not getting that with five months left on a contract.
"What does Robbie mean by 'big money'? I've not got a clue, but, for me, if you were to get an offer of half-a-million, maybe over that, that would be a fair offer.
"But I still think they have to weigh everything up.
"What does it mean if they lose John Souttar, in regards to who replaces him and what effect it'll have on the team and what they're trying to achieve in the second half of the season?"
Meanwhile, Chris Sutton has described the Scotland international as a “downgrade” in comparison to Connor Goldson who is set to leave Rangers at the end of his deal in the summer.
“I think that he’s a good player,” the former Celtic player told BT Sports Scottish Football Extra.
“John Souttar is a right-sided centre half, the issue with Rangers is what is going to happen to Goldson, it looks as though he wants to jump ship.
“Is he like for like for Goldson? I don’t think he’s at Goldson’s level, not that Goldson has been exceptional this season.
“With respect to John Souttar, I think it’s a downgrade.”