McManus was a product of Chester City's youth system and a prolific scoring record for the youth and reserve sides persuaded Bobby Williamson to hand McManus a professional contract on 2 October 2007.
Highlights of his early time at the club included scoring the shock winner for Chester's youngsters against Tottenham Hotspur in the FA Youth Cup in December 2006 and a hat-trick against Carlisle United in a reserve fixture in September 2007.
He made his Football League debut as a late substitute in a 3–1 home win over Shrewsbury Town on 7 October 2007, becoming the first player born in the 1990s to make a first-team appearance for Chester.
He made his first starting appearance in the first–team in a Football League Trophy tie away at Carlisle United two nights later and remained in the first–team squad for most of the season.
In the closing weeks of the 2007–2008 season he played regularly in attack, scoring his first league goal in a 2–1 loss to Lincoln City on 12 April 2008.