Sundowns earlier confirmed the capture of the Ghanaian goalkeeper on a five-year deal following his exit from Córdoba FC in Spain.
The 30-year-old, who played in the 2015 AFCON final loss to Ivory Coast, has also plied his trade for CD Tenerife, Guadalajara and Mirandés among other sides.
"I can confirm that we have signed the player," said Downs spokesman Thulani Thuswa. "We are expecting him to land today and join up with the guys in Rustenburg."
The African champions are spending the week in the North West Province as they prepare for their MTN8 opener with Maritzburg United at Lucas Moripe Stadium on August 13.
Brimah's arrival at Chloorkop offsets the recent departure of fellow keeper Wayne Sandilands to Orlando Pirates. Ugandan shot-stopper Denis Onyango currently commands the number one jersey at Masandawana, ahead of Zambian Kennedy Mweene and Thela Ngobeni, who has returned to Tshwane following a successful loan spell at Free State Stars last term.
However, Brimah's acquisition raises foreign quota issues as Pitso Mosimane's roster includes Ricardo Nascimento, Fares Hachi, Yannick Zakri, Leonardo Castro, Bangaly Soumahoro, Mogakolodi Ngele, Kudakwashe Mahachi, Cuthbert Malajila and Fiston Razak.
Thuswa declined to comment regarding this matter and on the club's immediate plans for Brimah.