The 19-year-old Belgian played for the Saddlers in the second half of last season - with four goals in 18 appearances.
"This signing is a big boost for us," boss Dean Smith said. "He first came here at a time when we needed a bit of quality and he certainly brought that to the team.
"He did extremely well for us and it's been an ongoing process since the end of the season where we've kept in touch with both Flo and Stoke. It's a big compliment that Stoke believe this is a good place for one of their up and coming talents to come and further his career in the game.
"His return has given everyone a real lift and I'm sure that like me, the supporters will be delighted to see Flo back in a Walsall shirt.
"The deal is initially for six months with a view to extending it further."