Dick Advocaat has conceded that he would like to make three or four more additions to his squad this summer.
However, the Dutchman has insisted that further recruitment is required before he can be satisfied with the options that are available to him.
"We have two new players with Coates and Matthews, but hopefully we will still get some other ones in as well," he told reporters.
"We still need three, maybe four [signings]. It's still very quiet in the transfer market in England, which is strange. We still hope we can get three extra players in the squad, which will make everything a little bit easier."
Sunderland will begin their 2015-16 Premier League campaign away at Leicester City on Saturday, August 8.