"If David comes here it would be an unbelievable signing for us," Johnson told the Lancashire Evening Telegraph.
"He's been linked with all the big clubs in the past and to be honest I'm surprised that the top three or four haven't come in for him because he wouldn't look out of place with one of them.
"I've known about our interest for quite a while and, yes, we have talked and he has asked questions about the club.
"He knows how much I've enjoyed it since I came here. I'm not saying that has anything to do with it but he seems very keen to join us, which is good from our point of view."
