Yoane Wissa has urged Brentford to "keep their word" and allow him to leave before Monday's transfer deadline.
In a post on Instagram on Sunday, the 28-year-old claimed the club has "significantly changed its position" having previously "put in writing" that he could depart should a fair offer be made.
Newcastle had an offer of £35 million ($47.26m) plus add-ons rejected earlier in August for the forward who scored 19 Premier League goals last season.
"Earlier this summer, I held open discussions with the club's senior management, including key directors and the new head coach," he said in the post. "I made clear my intention to explore a new challenge.
"During these conversations, it was confirmed to me and my representatives that the club would not stand in my way if a reasonable offer was received. This was also put in writing.
"Yet as the window comes to an end, the club has now significantly changed its position, going against what was communicated.
"This has left me in a difficult and frustrating position. The commitment that I could leave this summer has not been fulfilled.
"In the meantime, I must do what I feel is right for my career and family and insist that Brentford honor, keep their word to let me join a new club and at a fair price."
The PA news agency has contacted Brentford for comment.
Wissa has not played this season, with head coach Keith Andrews explaining his omission following last week's win over Aston Villa by saying he wanted his players to be "absolutely committed."
It was reported in July that the player flew home early from the club's training camp in Portugal after making clear he wanted to join Newcastle.
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He has not been training with the rest of Andrews' squad this season.
Wissa added: "Being made to stay beyond this summer will only tarnish four wonderful years at this incredible club and so l ask Brentford's owners and directors to now keep their word to let me leave in the final hours of the window."
Newcastle announced the signing of Nick Woltemade from VfB Stuttgart on Saturday but remain active in the market amid the ongoing transfer speculation surrounding star forward Alexander Isak.
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