The Saddlers have handed 17-year-old Mukuna a one-year deal following a few months with the club on trial.
He was not included in the squad for the 1-1 draw with Colchester United on Tuesday night and is yet to make a senior appearance in his young career – having previously been on the books of Sutton United.
Flynn, though, insists giving the youngster a chance to develop is a low-risk move for Walsall.
“Jonas was somebody who did fairly well over pre-season,” said Flynn.
“He’s a very determined boy. He’s built like a man – strong in his running stats and everything.
“He’s one where it was a very, very cheap option to cast a further eye over him and watch improve in men’s football full-time.
“Whether or not he goes out on loan just to play men’s games is a different story, but Jonas was a no-brainer in terms of that it’s not a gamble, really, with the wages and his age.
“It’s a good fit and gives him an opportunity to earn a professional career.”