The 29-year-old has featured just once this season, with Siwelele undergoing major changes following the sale of SuperSport United and a looming relocation to Bloemfontein.
Mbanjwa initially joined SuperSport from the now-defunct Moroka Swallows to provide competition for first-choice keeper Ricardo Goss.
Under coach Gavin Hunt, he pushed hard for a starting berth and remained a reliable option for nearly two years.
This campaign, however, he has been on the bench in four of Siwelele’s five Betway Premiership fixtures, starting only once under Lehlohonolo Seema, as the club continues to struggle for results.
Arrows, meanwhile, are three points better off than Siwelele but have also looked vulnerable at the back.
Coach Manqoba Mngqithi has rotated between Nkosingiphile Gumede, Xolani Ngcobo and Edward Maova, with none of them making the No.1 jersey their own.
Arrows have conceded six goals in five league matches and sit ninth on the table.
Mbanjwa’s move is believed to be close to completion, giving Arrows an experienced alternative as they look to stabilise defensively.
For Siwelele, the departure means the goalkeeping responsibilities will now rest with Ricardo Goss and youngster Samukelo Xulo, who was recently called up to Bafana Bafana’s CHAN squad for matches in Tanzania and Uganda under coach Molefi Ntseki.