Thorgan Hazard's loan destination was in doubt, but it appears to have been decided recently. According to Kristof Terreur, the younger brother of Eden will be returning to Zulte Waregem for a second go-around with the Belgian club.
There had been rumors that Hazard was in demand, and that Anderlecht were keen on acquiring him for the year. That seems to have fell apart because the top club in Belgium wanted an option to buy, something they certainly weren't going to get from Chelsea.
That left similar-quality options in Genk, Zulte, and Middlesbrough as the frontrunners for Thorgan's services, and it appears the club and player have decided to go with the familiar route and send him to a place where he's already established himself. He should get loads of minutes right away at Zulte, where at the other clubs he'd probably have to prove himself all over again. Given the options it seems were most available, I think Chelsea probably took the best one.
Some will complain that he's "too good for Belgium" at this point, but frankly, I just don't think this is true. He's certainly one of the better players in that league, but he's only been playing first team football for a year and another season worth of assured minutes might be the best thing for him.