Man Utd boss Ferguson: Ferdinand desperate for FA Cup
Fergie said: "Rio mentioned it last year in the dressing room before we went out against Liverpool. He said, 'Right, I've never won this cup' so it means a lot to him.
"The cup is a tournament where form doesn't necessarily win the games.
"Luck has a lot to do with cup football. We got to a semi-final against City and over the last few years we've had some hard draws.
"Twice away to Liverpool, away to City, a home tie against Leeds and we thought we could rest a few players and got caught short.
"Now it's West Ham and this is a particularly hard one.
"They're in good form, particularly at home. We won't make too many changes."