Dick Advocaat says Jeremain Lens can provide the creative flair Sunderland were missing last season and help improve their form in front of goal.
The Netherlands international moved to the Stadium of Light in July after Sunderland agreed an undisclosed fee with Rubin Kazan, and has impressed during pre-season.
Lens is in line to make his Premier League debut against Leicester City on Saturday, and Advocaat believes the 27-year-old could prove to be a key addition.
"We had a problem last season making goals and also creating chances, so something was wrong in both midfield and up front and that's why we bought Lens," said the veteran head coach.
"He is a very good addition who has pace and can score goals. If we can play attacking football then we have the players who can do that."
Yann M'Vila is Sunderland's latest new signing but he is unlikely to be the last man through the door at the Stadium of Light this month.
Advocaat added: "We have brought in players who improve the squad. Too many players last season were very sure of their position and that is more difficult this season.
"We have brought in five players and Connor Wickham has gone [to Crystal Palace], and we still hope to bring in one or two players more.
"The most important thing is that you have competition - that everybody has to fight for their places. You can see now in training that that is improving."
