The Magpies' second-string host their League Two opponents on Tuesday night at the club's home ground as they aim to reach the last 16 of the competition.
United's qualification from Group G was achieved a 100 per cent record - the only academy side to manage the feat - after recording away wins at Doncaster Rovers, Grimsby Town and Notts County.
And, following Newcastle's 2-0 victory over Leeds United Under-23s in the Premier League Cup on Friday night, their third successive win, Longstaff and his team-mates are looking to build on their impressive recent run.
"Everybody in the team is really looking forward to the game on Tuesday," Longstaff told nufc.co.uk. "We were concentrating on the game against Leeds but in the back of your mind you've got a big match against Macclesfield at St. James' Park.
"We have such a good group of lads and I think everyone will be relishing the opportunity to play in the game and we're looking forward to the test.
"Hopefully we can get a strong attendance. It will be nice to show the fans we are a good side and hopefully we can perform on the night to prove that."
Coach Ben Dawson has mixed up his starting line-up in the last two games, making five changes in each, and Longstaff - whose older brother Sean penned a new four-year deal with the club this week - admitted that the majority of the squad will be fighting for their place against the Silkmen.
"We played last Monday night (against Stoke), where we brought some lads into the side who did very well. On Friday, we have brought in more players who have also performed so it will make the team tough to pick with everyone playing well and winning matches.
"We have good players in all positions so even in training sessions you are trying to be better than your team mates and get into that starting line-up on Tuesday.
"However, it won't be just the eleven on the night that will go for the win, it will involved those coming off the bench. If we can stick together as a team, we have a good chance of progressing."
Admission on Tuesday night will be via the East Stand, with prices set at £5 for adults and £1 concessions. Season ticket holders and members do not gain free admission for this game.
The match will see former Newcastle defender Sol Campbell manage Macclesfield for the first time.
