The England shot-stopper will be out of contract at the end of the month and it is understood he has not been able to agree an improved contract with the Hammers.
The 32-year-old has reportedly been under-paid for many years and was hoping for an improved offer of around £50,000 per week. The Hammers are simply unable to afford that kind of contract for a goalkeeper entering the later years of his career.
Hammers co-owner David Gold said on Twitter, ““Robert Green is a free agent he has chosen to move on. Matthew Upson did the same thing.”
“Nobody wants Rob to leave but nothing is for ever, he must do what is best for him and we must do what is best for us.”