Director of Football Julia Setford said everyone at the club had been left shocked and saddened by Katie Sheppard's sudden death.
Katie was an absolute West Ham fanatic, she had a Season Ticket and it was her absolute ambition to play for West Ham Ladies. When she was at training, she was the bubbliest person and just fantastic to have around the club.
She joined us when she was 17 and played for the club for two seasons. Katie was a central midfielder and she made a couple of first-team appeatrances under me before she went off to university.
Katie was a fantastic person and a lovely kid. It is such sad news for us all. The club will certainly be a lesser place without her.
West Ham United ladies player Katie Sheppard has died, aged 20. Katie first played for West Ham's under-19 side before making her first-team debut as a substitute in an FA Women's Premier League Cup tie in November 2012.
In a statement, the club said:
"It is with great sadness they we have to report the untimely passing of Katie Sheppard. She had played for the Ladies team for the past two seasons, a true Hammers fan and season ticket holder at Upton Park. We send our condolences to all her family and friends at this sad time."