Siwela is the only South African match official that will be travelling to the World Cup, set to kickoff in June.
Enoch Molefe and Jerome Damone were the last local match officials to participate in the World Cup which was held in South Africa in 2010.
Mosimane, who rates Siwela highly, says the assistant referee deserves to officiate in Russia.
"I want to congratulate Zakhele. It’s been long since we had someone in the World Cup,” said Mosimane.
"This one knows the line. When we see Zakhele we are happy at Sundowns. Percy [Tau] becomes happy and he says I can always break all the time because he manages the line properly.
He continued: "It’s good. The last time we had someone in the World Cup was in 2010.”
Siwela had a good game on the sidelines as Sundowns beat Chippa United 2-0 at Loftus Stadium on Wednesday.
The victory ensured Sundowns kept their place at the top of the standings and they will next face Baroka FC at Peter Mokaba Stadium on Sunday.