The 20-year-old spent last week undergoing trials in Russia, where he seemingly impressed enough to be offered a full-time contract.
The centre-back's agent has confirmed the Brazilians are considering their options, and will come back with a decision by "the end of the week".
"The trial went well and Siyanda did quite good," Xulu's representative, Paul Mitchell told The New Age.
"The team was very happy with what they saw and they sent through an offer and now we are still waiting to hear from Sundowns president Patrice Motsepe in the next coming days.
"We still have to discuss a couple of things, but what I can say is that negotiations are promising and I am hopeful that by Tuesday or the end of the week we will have something."
Sundowns look likely to allow the youngster to leave as they have already made moves to strengthen their defence following the signings of Alje Schut from FC Utrecht and Wayne Arendse from Santos.