The young goal-getter has netted only twice in his time at Upton Park and is due to return to Liverpool once Alan Pardew's promotion-chasers are eliminated from the FA Cup.
"I'm a bit gutted. I'm all packed and can't wait to get back, but hopefully I'll be able to come back next week," revealed Mellor.
The first-division side entertain London rivals Fulham at Upton Park in a fifth round replay for the right to face Manchester United at Old Trafford in the last eight.