Leeds United are also looking to bring in another forward before the close of the transfer window.
Leeds are still eyeing up another three new additions this summer, with defenders and attackers wanted.
Leeds are keen to bolster their squad, but it is strengthening their backline which is their immediate priority.
The Whites have limited options in the heart of their defence, with just three natural centre-backs in their current squad.
Leeds have added Matthew Pennington this summer, on loan from Everton, but Liam Cooper and Pontus Jansson are the only two other senior centre-backs currently available to Christiansen.
Leeds are now said to be working to push through a deal for a defender, before the season starts.
Christiansen also wants another forward, but reportedly feels more comfortable with his current options in that position.
The Whites kick off their campaign with a match against Bolton Wanderers at the Macron Stadium in early August.
Receive exclusive football transfer news and updates twice a week to your mailbox
