The club signed Almiron and Barreca last week.
Almiron, signed for a club-record £21million fee, could make his debut against Wolverhampton Wanderers at Molineux on February 11.
Barreca, meanwhile, came off the bench in Saturday’s 1-0 defeat to Tottenham Hotspur.
Benitez was short of attacking options at Wembley, where he needed fresh legs as Tottenham pushed for a goal late in the Premier League game.
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And United’s manager believes Almiron, a No 10, and attacking left-back Barreca will give United another dimension when the team is under pressure.
“I think that in these kind of games you know you have to defend, but also our ideas was to go forward when we could if we regained the ball,” said Benitez.
“We did it during the first half when we had two or three situations that were very close, and especially in the second half when we started with one or two crosses, one of which we hit the post from.
“We also had a chance for Ayoze (Perez). You have to defend against good teams like Tottenham, but, after, you have to think about attacking as well.
“These players, Barreca and Almiron, both are offensive players, they’re fine on the ball, they go forward, they have some pace, and they bring us something that we needed.
“So, hopefully, they can help the team in attack.”
Asked if Almiron’s arrival had lifted the dressing room, Benitez said: “I think everyone was expecting new faces.
“Barreca and Almiron, they’re good on the ball, they can play with some pace and they are offensive players.
“Especially because Miguel Almiron’s playing as a No 10, he’s used to playing in this position, so he gives us the competition we were looking for in this position where we didn’t have too much.
“Hopefully, it will be good and everybody will continue working as hard as they do now, but with more confidence.”