Nascimento recently returned to Chloorkop after contract termination talks dragged on while he was recovering in his native Brazil from a hernia operation.
Sundowns opted against registering Nascimento this season due to his injury and foreign quota issues, with the deal he penned set to expire at the end of the campaign.
However, Mosimane says the player is now unattached despite his training with the Tshwane giants.
"He is strong, getting there but he is not registered with us. We can't talk about him, he is not registered," said Mosimane.
"For us to register him we want to create space. He can go to anybody, he is a free player."
He added: "He is a free player but he likes the team. He wants to stay."
Downs have registered new Ghanaian signing Razak Brimah, Colombian striker Leonardo Castro, French wingback Fares Hachi and Ivorians Bangaly Soumahoro and Yannick Zakri as their five allotted foreigners.
While Castro has been linked with a move to Kaizer Chiefs next term, Masandawana are also known to have their eye on Uruguay winger Gaston Sirino and Bolivian forward Gilbert Alvarez Vargas.
Mogakolodi Ngele, Cuthbert Malajila, Khama Billiat, Denis Onyango, Kennedy Mweene and Anthony Laffor have been naturalised.