Maguire was impressive for United's opening night win.
He told manutd.com: "I feel good, I feel fit. Physically and mentally, I'm in a good place and yeah, I'm looking forward to a big season.
"There's so many games this season. I'm sure there's going to be a lot of changes to come, game to game, in the starting eleven. And when your turn is upon you, you need to take your chance. And yeah, it's one that we'll need a big squad for.
"For myself, I feel fit and ready to go and looking forward to the season."
Maguire also said: "Obviously, we want to be in the Champions League spots. We missed out this season as we weren't good enough in the league.
"I think we don't really want to set any targets - I think this club demands trophies. So we want to win another trophy, of course, and in the Premier League we know there's large improvements that we need to do and make from what we did last season.
"For sure, we've got to improve on last season and let's see where it goes and takes us."