The Hammers have appointed Julen Lopetegui to replace the departed David Moyes.
Sullivan knows that after a change in head coach, fans will be expecting the team to start the new season all guns blazing.
Sullivan told The Sports Agent Podcast: "It is very strange that at the start of the summer the manager transfer market is more interesting compared to the players' one.
"Obviously, Lopetegui has come in and I met Julen last week for the first time and he seems very much up for the challenge, full of energy and as I said to him, we've got a few weeks on everybody else so there is no excuse to not have a good pre-season, which is good.
"He's come with a great pedigree and a point to prove after obviously leaving Wolves a bit prematurely to what he would have liked. He's been in Spain with Real Madrid and won the Europa League with Seville, so we're excited to work with him."