The Magpies have been active in the transfer market since the end of the 2013-14 Premier League season, having already brought in six new players, including Siem de Jong, Remy Cabella and Jack Colback.
However, the manager told the Shields Gazette: "We had to be patient after the [Yohan] Cabaye sale [in January]. We couldn't get it in that window, which was unfortunate. It made us finish without an offensive source.
"We've tried to spread the net a little bit and spread a little bit more quality around the team. It's a combination of a lot of work.
"We still have a bit of work to do. At the moment we've got a healthy squad, which we're looking to increase."
Four of the new signings are currently with the squad in New Zealand for pre-season preparations, while Cabella and Daryl Janmaat will link up with the side later this month