The Argentinian was named Palace's player of the year last season and has started the new campaign in the same impressive form.
"I am surprised there hasn't been a bid, he's a great goalie," said Derry.
"I've played with a number of good ones in the past and he is right up there.
"Who knows what is going to happen though? We don't want to court bids for him but we know everybody has their price.
"Julian wins us games single-handedly at times and he's a great goalie to have, and a great guy as well."