Sadler made more than 50 appearances for the Saddlers last season after he was released by Watford.
Dean Smith's side will arrive at the Broadfield on the back of an 11-game winless run but Sadler knows promotion-chasing Crawley will have to be on their guard.
"Dean is a great guy and a very talented young manager and he won't let their heads drop or their standards slip," he told the club website.
"There have been quite a lot of changes in personnel there since I left in May but they still have some very good players. It is going to be another tough game.
"We have seen all season what little there is to choose between teams at the top and the bottom of this division but we have two home matches coming up and if we can produce two solid home performances there's no reason why we cannot come out on top."