Wing-back Weah and winger Mbangala were left in the stands for Juve's Club World Cup defeat to Manchester City on Thursday.
Asked about the pair's absence after the 5-2 loss, Juve coach Igor Tudor confirmed: "We preferred not to call them up for market reasons, that's enough."
TMW says Forest's €25m offer for Weah and Mbangala has been accepted by new Juve GM Damien Comolli. However, the decision has left the players blindsided.
Indeed, USA international Weah's agent Badou Sambague took to social media to blast: "Weah is a fantastic player and a fantastic teammate.
"Seeing people behave like this for money and selfishness has disappointed me a lot. It's a shame. In any case, until I'm here, no one can treat one of the players I take care of by sending him left or right like a puppet. I'm happy that Timo has a great education and a personality that allows him to stay focused on the games."