The pair played together for a year in 2010-11 as Mignolet enjoyed his first season in English football.
"If you've seen training, and the game the other day, you saw he's a very good goalkeeper," Henderson told LFCTV Online.
"He's a very good shot stopper and, to be fair, he can do anything.
"He's very good with the ball at his feet, has got good kicking and distribution, and his shot-stopping is unbelievable.
"It'll definitely be interesting. Pepe [Reina] is an amazing 'keeper, everyone knows that, so it'll be good competition for them both."