Johnson, 29, scored 15 goals during the first half of the season before returning to parent club Mansfield Town on January 15 - the day after earning Walsall a point at Tranmere Rovers.
And despite trying to strike a deal for the forward to come back to the Poundland Bescot Stadium permanently, the Saddlers were ultimately priced out of the move.
Writing on Twitter, Johnson said: "I would like to thank everyone at Walsall for my time at the club, I’ve loved it. A club I’ll always look out for now. To the fans you’ve been amazing from day one. Get behind the staff and the lads for the rest of the season and I hope you have a strong finish! #Saddlers"