Paul Pogba, Zlatan Ibrahimovic and Marcos Rojo all returned from injury recently and Rashford says having them back is a huge bonus with a run of tough fixtures coming up against Watford, Arsenal, CSKA Moscow and Manchester City.
Pogba scored on his return to the team in the 4-1 win over Newcastle, while Ibrahimovic has come off the bench in the last three games.
"Not even just thinking about football, but thinking about them personally too, it's hard to see your team-mates out for so long," Rashford told 'MUTV'.
"To have them all back now has brought a really happy vibe to the squad.
"I'm sure they're all really happy to be back playing again, and if we can keep winning with them in the team, it keeps everything rolling on."
Herrera echoes the thoughts of his team-mate, and is glad to have a fully fit squad available as United look to reduce the eight-point gap between themselves and Premier League leaders Manchester City.
He said: "It's great to have them back and, with them [in the squad], we are stronger.
"Marcos was amazing against Basel - you cannot see the difference between before the injury and now, he's worked fantastically hard to come back.
"Zlatan is going step by step because the injury he had was even worse, and Mike [Carrick] is going to be back soon, too. With them, we are stronger, and, with them back, we are optimistic of fighting for every title this season."
The Spanish midfielder is looking forward to the busy period of games, with the prospect of more playing time, although Jose Mourinho is expected to rotate his United squad.
"I think it's the best thing you can have," he said. "As a footballer, you want to play as many games as possible, you want to be part of the team always. We have a lot of players, a lot of quality and a lot of games, so it's fantastic for all of us."
Rashford added: "It's great to have all the games and, while we prefer to take it one game at a time when it's so busy, by the time it gets to Christmas, it calms down a bit and you can start to see pathways to certain tournaments and certain trophies."