Cahill is joining the MLS outfit in a £1 million deal.
"Talking about Tim Cahill, he's going to be great," Henry said. "We're going to have to wait for him to go through the medical. He's going to be a great asset for us and also for the league.
"If you saw the guy play the way he plays, I love the commitment and I always loved his commitment.
"He's great in the box, his headers are unbelievable. He fights back to the net and his football IQ is great also. Hopefully that can be a plus for us."