Manchester City would be interested in signing Raheem Sterling if he were to become available, according to Sky sources.
Tottenham have completed a deal for Cologne defender Kevin Wimmer and he will join them in June, Sky sources understand.
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.