Celtic sold playmaker Mahlasela to Kaizer Chiefs as part of a trade that saw defender Gordinho go the other way on a one-year loan deal.
Konco told his club's website: "Lorenzo has proven his worth since his first PSL appearance. He is such an industrious and a resolute type of defender. Signing him will bring more stability in our already reliable defence.
"Yes, we have lost one sensational player in Mahlasela, whom we negotiated with to remain at Celtic but he was set on joining Kaizer Chief and we wish 'Skipper' all of the best.
"Our plan is to make sure we solidify every department with quality players, hence the arrival of such diligent players."
Siwelele also have their eye on Baroka attacker Siphelele Ntshangase, while they recently recruited former Orlando Pirates midfielder Menzi Masuku from Chippa United.