Dave Jones has told Rangers manager Walter Smith that it will take a good offer to prise Glenn Loovens away from Cardiff.
The 24-year-old defender has been identified as one of Rangers' top transfer targets and Smith had him watched on Tuesday as Cardiff beat Vitoria Guimaraes 2-1 in the Algarve Challenge Cup.
Jones has yet to receive an approach from the Scottish club but has warned Smith that he would only consider letting Loovens go for the right price.
"If Walter wants him then make a bid but, like any of our players, he won't be cheap," Jones told the Scottish Daily Mail.
"Walter's got a big decision if he wants to come in for him.
"We have had no official contact from Rangers but, listening to what other people are saying, then who knows?
"We were told they had someone here to watch our game."
Rangers will have to move quickly if they are to bolster their squad before Thursday's UEFA Champions League deadline, ahead of next week's qualifier against FBK Kaunas.
However, assistant manager Ally McCoist has assured fans that Rangers are actively pursuing new signings.
On Loovens, McCoist admitted: "It's not moved on at all to be honest with you.
"But we are still looking at one or two players.
"If the opportunity arises to strengthen between now and the start of the season, we will obviously do that.
"If it doesn't, we will just have to get on with what we've got for next Wednesday.
"If good players come up and they are available and we can afford them, we will certainly be in the market for them."