The Hammers have already landed Argentine Mauro Zarate this summer and Sullivan, along with fellow co-chairman David Gold and manager Sam Allardyce, is desperate to improve their underachieving squad from last summer.
Allardyce has promised fans a more attacking outfit will take to the Upton Park next season but the club currently have no left back and just three central defenders in the first team squad.
Sullivan wants to improve all areas and believes this new addition will get fans back on side.
“We’ve been working extremely hard to bring in the players we know we need to improve the squad ever since the end of the season, and I believe we are very close to putting the finishing touches on a transfer that will excite us all” Sullivan said.
“Should we land this player, we would have had to beat off competition from some of Europe’s top sides, and for me that shows the direction we are taking as a Club right now.
“We all know we need to improve from what we achieved last year, and this summer’s recruitment is going to be key to that.
“We have already made what I am sure is going to prove to be an outstanding signing to increase our firepower up front, and we will make several more across the board as the summer goes on.”