Celtic claim a fee was agreed with Manchester City for John Guidetti prior to them taking the striker on loan.
Xabi Alonso claims no Premier League offers were put to him before leaving Real Madrid for Bayern Munich.
The 19-year-old midfielder, son of Sunderland manager Gus, is a graduate of the Charlton academy and was voted Player of the Year last season despite only making his debut in January.
He turned down the offer of a new contract with the Championship side earlier this summer amid widespread interest in his services.
Charlton will be due compensation for Poyet as he is the under age of 24, with a tribunal settling the fee.
West Ham have already signed Mauro Zarate, Cheikhou Kouyate and Aaron Cresswell this summer.