The Spaniard is adamant that more quality needs to be added to the ranks at St James' Park if the club are to progress this season, particularly after back-to-back pre-season defeats to Sporting Braga and Augsburg.
Yoshinori Muto, Ki Sung-Yeung, Fabian Schar and Martin Dubravka have all joined the club so far this summer, but Benitez is hopeful they won't be the last.
"We are trying to improve things," he told 'Sky Sports News'.
"We don't have too much time but we have to try until the last minute of the transfer window to do the best for the team.
"I don't know if we can finish, or not, the deals. We are working, trying to improve the squad for the first game of the season.
"Hopefully we can do something and it will be positive, because you have to increase the competition and improve the squad.