The attacking midfielder made his unofficial debut for Bucs during their 1-0 defeat to Kaizer Chiefs in the 2017 Carling Black Label Champion Cup match on Saturday.
Isolezwe's source at Celtic has since disclosed how Nyatama ended up leaving Phunya Sele Sele for the Buccaneers during the current Transfer Window.
"The decision to sell Nyatama made business sense," the source said.
"Celtic wanted to keep him, but they realized that they could not afford to turn down Pirates' lucrative offer," the source continued.
Bucs were also heavily linked with Celtic midfielder Alfred Ndengane, who is one of Phunya Sele Sele's key players.
"Pirates paid R5 million for the player. They intially wanted Alfred Ndengane, but Celtic refused because they wanted to keep him," the source added.
"With Musa, they realized that although they still needed him, he was worth selling because he is ageing," the source concluded.
Nyatama, who scored five goals in 28 PSL matches last season, will turn 30 in two weeks time.