The Merseyside club have confirmed that a fee in the region of £1m has been reached with Major League Soccer side New York Red Bulls.
"I'm not overly surprised," Unsworth told BBC Sport. "I don't think his form over the last six months has been what it used to be. He's been a fantastic servant for Everton - a bargain buy.
"He's scored many goals but his form has just waned a little bit. I'm sure he goes with everyone's best wishes. I think it suits all parties. Tim has been linked with a move to for the last six months. I don't think Everton fans are surprised."
Cahill has spent eight years at Goodison Park.