Omar, who has penned a six-month deal which includes an option to extend in the club's favour, joins from KV Mechelen after spending around a month training with the squad as manager Dean Keates considered his options.
Mussa, who has made appearances at various levels for the Belgium national side, is keen to make the most of his opportunity at Banks's Stadium, with a view to earning an extended deal.
Speaking via the club's official website - Saddlers.co.uk - Omar said; "I’m very happy to sign for Walsall and I am excited to start life here. I’m very ambitious and I can’t wait to get going. My aim is to help everyone and hopefully get in the team and earn myself a longer deal by impressing the manager.
"I like to keep the ball. I play in the gap just behind the striker and I will always look to create opportunities for my teammates or for myself. I hope I can add goals to this team and give the fans a good feeling.
"I have been welcomed in by everyone from the first minute I arrived here. Everyone here wants to give you confidence, they want you to succeed."