He revealed on Friday that the 29-year-old has been on his radar for a while.
"Yes, for a long time," he said. "I've known him since he played for Paris Saint-Germain.
"He is one of these players who never had the luck in his career to be completely playing in a consistent way in the Champions League. You feel, if he has that opportunity, he can show how good a player he is.
"I think he had the Spanish qualities but because he has played for a long time in England I'm quite amazed how strong he is in the challenge as well.
"He had a good education in Scotland so he is strong in the challenges."