After a 1-0 defeat at Old Trafford courtesy of Juan Mata's second-half strike, Nuno's side are five without a win in all competitions.
He has constantly stressed the need for fresh faces over the past few weeks, and he hammered the point home again after losing the third-round replay.
"We are working on it. I would like it to be ASAP, of course," said Nuno.
"But things take time. Things take time. It's like that."
The need for attacking reinforcements this month has been heightened by the departure of Patrick Cutrone – allowed to return to Italy just six months into his Wolves career.
He scored on his first start for Fiorentina today, while Nuno is on the lookout for at least one forward player before the window shuts. Reports in Ecuador suggest a deal for 19-year-old Leonardo Campana is close to being done.
Nuno's small squad may be even lighter after Ruben Vinagre was seen to be struggling after the final whistle.
The Portuguese will now be assessed by the club's medical team, while Adama Traore – who looked a little uneasy as he was substituted late on – is thought to be fine.
"Traore is OK. Let's see with Vinagre. Let's assess the situation," said Nuno.
Wolves had their chances against Ole Gunnar Solskjaer's charges.
Pedro Neto thought he had opened the scoring early on, but VAR intervened and disallowed his goal because of a handball from Raul Jimenez in the build-up.
"I haven't seen the situation, but that is VAR," said Nuno.
"Even we don't celebrate. Old Trafford celebrates a non-goal.
"It's VAR. It is wrong. What can we do? I'll see the images."
Matt Doherty also hit the woodwork for Wolves against United with a close-range header.
United, though, were not seriously troubled in the second period and got the win as Mata beat the offside trap and chipped the ball over John Ruddy, who had done well to save two Daniel James efforts in the first half.
"I think it was good. We performed well, in both halves. Defensively and offensively," added Nuno.
"We had good chances from good combinations. United also had chances. It was a good game.
"When you go out of a competition, you are sad and frustrated.
"But how we did it, how we played, can move us forward. Let's try to sustain this level of performance – and let's take our chances."