The 29-year-old right-back, the Eagles' longest-serving player, spent the end of last season on loan at Charlton after losing his place to youngster Nathaniel Clyne.
"There is a possibility we will make Danny available because of Nathaniel Clyne coming through," Warnock told the South London Press.
"I've really got to look at areas I want to improve and it may mean letting one or two players leave without damaging the squad. Danny is too good to not be playing regularly."
Butterfield has 12 months left to run on his current deal at Selhurst Park.