The Toffees won 2-1 at Goodison Park thanks to a first-half brace from Leighton Baines with one coming from the penalty spot and there was no way back for the Baggies despite Shane Long's goal.
Moyes wants to bring in players to boost his team's push for a top-four finish but Holland international Fer will not be among them after problems emerged in his medical.
"Yes, it was disappointing," the Scot told Sky Sports. "I'm disappointed for the boy and I'm disappointed for our players because they're looking for me to add one or two new faces.
"It's just the circumstances didn't work and it happens in these deals at times. It's all part of the situation - the contract, the medical, everything about the thing has to be right before it can be completed."
Asked if he has time to sign someone else, Moyes said: "We've only got a day. We'll try. We'll see if there's anything we can do to help the lads if we can. I want them to feel we're doing everything we can here to make it work.
"I'd think it's probably more unlikely than likely but we'll have a go at it."
Moyes was coy on Everton's hopes of making the top four as he preferred to focus on the first objective - passing the 40-point mark that usually ensures Premier League survival.
"I think that might just have made us avoid relegation if we are lucky - 41 points," he added. "For most teams, maybe one or two don't, but for most that's always the first part.
"And it's well done to the players for getting to that points total at this stage of the season. They're going well.
"We know we've got to win more. We've drawn quite a lot of games. So in the second half of the season we want to win more games.
"We've had a decent January. We've had a few draws but we're picking up the points and like I've said before there's not much between the teams."