Several reports have linked with 28-year-old with a move to Newcastle and Wissa is understood to be very keen on joining.
Wissa has removed all references to Brentford from his social media, unfollowed the club, and changed his Instagram profile picture to black, a move seemingly in protest against the Bees.
Newcastle want Wissa to replace Alexander Isak who is also on strike as he tries to push through a move to Premier League champions Liverpool.
The striker was left out of the squad for Brentford’s 3-1 defeat to Nottingham Forest in their first league game of the season.
New manager Keith Andrews offered an update after the game, saying: "It is what it is. it's an ongoing issue. Ideally Wissa would have been available today and unless anything has happened in the last few hours then it's the same things.
“Hopefully it can resolve itself sooner rather than later. We're always looking and there's a clear plan at the club if a player leaves then we'll look."