A source close to Njau has told Goal he has already joined the Kisumu-based side and is set to be unveiled soon.
"Njau has already accepted a deal from Western Stima and his departure from Sony Sugar is all but confirmed. I am not in a position to state the length of his contract with Stima for now but for sure he is no longer with Sony Sugar," the source told Goal.
Western Stima have been quite busy in the leadup to the new Kenyan Premier League (KPL) campaign, having appointed Salim Babu as their new head coach.
Abdala Wankuru of Sony Sugar and Fidel Origa from Kariobangi Sharks are understood to be Stima transfer targets as well.
Njau is the latest to depart the Awendo side after head coach Patrick Odhiambo and midfielder Tobias Otieno left to join KPL champions Gor Mahia.
Odhiambo joined K'Ogalo as assistant to head coach Hassan Oktay.
Goalkeeper Kevin Omondo, midfielder Joshua Nyatini and striker Derrick Otanga have been confirmed at Wazito.
All the players who have left were key in the 2018/19 season when Sony Sugar finished fifth in the KPL.