Celtic and Rangers are both tracking Chelsea centre-back Tomas Kalas, according to reports in the Scottish media.
The Czech international is currently on his seventh loan spell away from Stamford Bridge, having spent the season at English Championship side Bristol City.
Kalas has helped the Robins to seventh in the table; just one point off the playoff places. His side have conceded just 37 times in 35 games this campaign which is the third best defensive record in the league.
The 25-year-old could, however, cost as much as £5m to recruit, with more than a dozen clubs said to be looking to secure the player’s services on a permanent basis.
Celtic will be looking to replace defender Filip Benkovic, whose loan deal from Leicester City expires in the summer.
With Dedryck Boyata’s contract also expiring at the end of the season, recruiting another centre-back will be a top priority for the Scottish club.