Slaven Bilic’s side took a second-half lead after France international Dimitri Payet scored a brilliant free-kick to beat United number one David De Gea.
The Hammers couldn’t hold on to book their place in the last four, though, after Anthony Martial finished from close range following a brilliant cross from Ander Herrera.
While Scholes felt United showed some green shoots of recovery against the Hammers, the retired England midfielder admitted Van Gaal’s side will struggle to beat the Hammers at their last-ever cup game at Upton Park.
Scholes told BT Sport: “It was a really disappointing week with two bad results.
“After a disappointing night at Anfield, you’d like to see the players come out and react. They did that against West Ham.
“The quality was missing in the final third of the pitch but to get a draw here, I’d like to think you’d win your home games in the FA Cup.
“It is a big opportunity missed because it will be difficult down at West Ham.”
The Red Devils’s 1-1 draw with West Ham brought to an end a two-game losing run for Louis van Gaal’s side.
The 20-time English champions host Liverpool in the second leg of their last-16 clash in the Europa League at Old Trafford on Thursday night.
United lost 2-0 at Anfield following goals from Daniel Sturridge and Roberto Firmino.
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