Rangers have rejected a second offer from Turkish club Bursaspor for versatile full-back Steven Whittaker.
Bursaspor, who signed striker Kenny Miller from the Scottish champions in January, had a bid for Whittaker knocked back earlier this week.
They came back in on Thursday night with an improved fee of £600,000.
Whittaker still has a year left on his contract and manager Ally McCoist is keen to negotiate a longer stay for the 26-year-old Scotland international.
"I have made it clear that Steven is one of the players I see as part of my long-term plans for the club," said McCoist after the first approach from Bursaspor.
"That is why we have opened talks with his representatives to extend his current contract."
Whittaker joined Rangers from Hibernian for £2m in 2007 and has been used at right-back, left-back, in central defence and in a variety of midfield roles.
McCoist was speaking after completing a seven-game scouting mission to South America.
"I and my staff have been recommended a few players from Argentina and this was a good opportunity to go out and have a look at some of them," he explained.
"I think I have seen just about all the top teams in the country - the likes of Estudiantes, River Plate, Argentinos Juniors, River Plate and Velez Sarsfield.
"It has certainly given me the chance to get a better handle on things in Argentina and it was a very worthwhile exercise, but I wouldn't say there is anything specific at this stage.
"There have been one or two players who have caught my eye and I might try to follow up a couple of things when I get back."