Masango completed a loan move to United from Danish side Randers FC until the end of the season.
Baxter worked with the Bafana Bafana midfielder at Kaizer Chiefs, where they won the PSL league title twice and two domestic cup tournaments together.
Bullet trained with Matsatsantsa in December during the festive break, prompting Baxter to dismiss reports that the player had signed for the defending Nedbank Cup champions.
“We have a nicely settled squad right now and were not really looking to bring in anyone mid-season, but when the chance came to sign Mandla, I had the confidence of having worked with him before.
“So I know he will adapt quickly and hopefully add an extra spark as we compete on domestic and continental fronts.”
The Bafana Bafana midfielder left South Africa in 2015 to join Randers after his contract at Chiefs expired and scored six goals for the Danish side.