He told whufc.com: "I would like to thank Hayden for his valued contribution. I wish him well and have no doubt that our supporters will give him a good reception whenever he returns. Gianfranco has been clear about allowing players on the fringes to get first-team football elsewhere if the opportunity arises and - given the fee, his age and his desire to play regularly - this deal is good for all parties.
"The manager has also spoken about improving the squad and I am working closely with him and technical director Gianluca Nani to make this happen. Any new arrivals will complement our blend of experienced internationals and homegrown youngsters. Our aim is simply to continue progressing in the league and the FA Cup, and build for the future at West Ham United."