Tottenham Hotspur are closing in on a club-record £35 million deal to sign Ajax centre-back Davinson Sanchez, sources have told ESPN FC.
Netherlands international Propper, 25, has signed a four-year contract and joins the Premier League club for an undisclosed fee.
Manchester United defender Cameron Borthwick-Jackson turned down Ajax before agreeing a loan move to Leeds United, sources have told ESPN FC.
Chelsea have announced that United States defender Matt Miazga will spend a second season on loan at Vitesse.
Ajax midfielder Abdelhak Nouri has left intensive care two-and-a-half weeks after suffering permanent brain damage having collapsed during a friendly.