The Spaniards have been impressed with the performance of the duo this season.
Bayer Leverkusen sporting director Rudi Voller insists there has been no official contact with any clubs.
“Nobody has made any official contact as yet,” he said.
“But it is no surprise that this sort of thing could happen with the quality we have in our squad.”
Castro’s contract expires in 2012 while Barnetta’s current deal expires in 2010.
“These offers don’t make any difference to us – we want to keep this squad together,” Voller added.
“Tranquillo wants to achieve something with the rest of the guys and we will try to get him to extend his contract.”
