The forward signed a six-month loan deal in the summer at the Championship club and he does not know where his next move will be.
Armstrong may return to St James' Park but he has impressed while on loan at Bolton and he has already made 18 appearances for the Trotters.
Despite only enjoying a brief spell under Benitez, the 20-year-old has been full of praise for the Spaniard and he is excited to work under him in the future.
He told Bolton's official matchday programme: "Rafa is a brilliant manager who has worked with some of the best players in the world.
"He’s just got a presence when he is stood in front of you, you can’t help but be taken in by.
"I’m enjoying my football at the moment. I’ve already seen an improvement in my game but I’m taking it each match as it comes. You can’t think too far ahead in football because it changes in an instant."