The Clarets were relegated from the Premier League last season with the Bafana Bafana striker contributing with three goals and one assist in 25 top-flight appearances.
The club are yet to adapt to the Championship and started their season with a 2-2 draw at home to fellow relegated side West Ham and a 3-1 defeat away to West Brom on Sunday.
Foster along with Hjalmar Ekdal and Andreas Hountondji are all expected to be moved on as Hayen continues to strengthen a team he inherited from Scott Parker.
"So I told you also last week, when there are players coming in we also have to make decisions on who is going out. With these players, that's something we have to discuss," Hayen told the Burnley Express.
"We knew, even from last season, that we need more goal threatening. One thing also, the new players who come in have also got to adapt to the level.
"You come here on a sunny day, noon kick off and early kick, so they have to adapt. Not only that, but also the intensity and then you have to increase your intensity."
Burnley are next in action against Bradford City in the EFL Cup on Wednesday.
