McCann marked his debut with a fine free-kick against Bristol Rovers on Saturday but is on international duty with Northern Ireland so will miss out.
Winger Nathaniel Mendez-Laing is a slight doubt after limping out at the weekend so former Nottingham Forest man Arron Davies could be handed a start.
Defender Gabriel Zakuani has a groin injury while midfielder Lee Frecklington (knee) and winger Chris Whelpdale (thigh) are also still not ready for the first-team.
Forward Lee Tomlin may be pushed into the starting line-up at London Road after completing his move from Rushden & Diamonds late on Friday, while manager Gary Johnson could also involve the likes of Steve Collis, Charlie Lee, Tommy Rowe, Carl Piergianni and Nathan Koranteng.
