Tau, who could win multiple accolades at tonight's PSL Awards ceremony at the Sandton Convention Centre, has attracted interest from overseas following his fine displays for club and country.
And Mosimane confirmed it is highly likely that the man who scored 13 goals and created as many assists in 2017/18 could be lost to South African football.
“It is not up to me, let's be realistic. He has done very well and we should expect somebody from Europe,” Mosimane said.
“There are talks already. I'm preparing that I'm losing him. It is going to be tough for us.
“But as I say always, tough when you lose 'CBD' and all that, we continued. We lost [Elias] Pelembe, Surprise [Moriri]. You lose [Katlego] Mphela, key players.
“Alje Schut was a captain and pillar of strength. But we have to replace.”
Meanwhile, Mosimane is still hoping he can persuade Billiat to stay at Chloorkop. The Zimbabwean playmaker has also been strongly linked with a move abroad when his contract expires at the end of June.
“I will do my best. If I don't sign Khama it is because he got a better offer somewhere. We can't let [him] go, he has been an important guy. I mean how many games has he played? He has been injured but look at the goals he scored, eight.
“It is important. This season was like his first, he was forever injured. He has been having injuries but you know when he comes in he scores the most important goals.
“Against Cape Town City it was a good, big goal. The goal he scored against Ajax Cape Town an equaliser, it brings you back. Very important, he scored in important games.
“He has been with us for long and sometimes you have to accept that they have to go, especially when they get good offers. But we have treated him so well.”