All you need to know about tonight's game
The Lions know that they will have their work cut out against a hard-working Cobblers side that have already beaten higher league opposition with a 3-2 First Round win over Colchester United.
But Millwall manager Neil Harris, who played at the old Wembley stadium in the 1999 AWS Final, is determined to get his players pumped up and ready for action as they aim to build on a 3-1 home success against Rochdale last time out at The Den at the expense of Chris Wilder's side.
Chopper's side go into action having tasted defeat on the road for the first time this season, a 5-3 loss at Peterborough United, whilst Northampton recorded a second away win in three on Saturday with an excellent 3-2 success at Wycombe Wanderers.
"We were deserved winners against Blackpool and Colchester and this is a game we can win if we are right and we play well. It is another tough test for us but it's a game that we will go and enjoy."
Jimmy Abdou (shoulder) and Ed Upson (knee) are both sidelined having sustained injuries in Saturday's match at Peterborough United, whilst Shaun Williams completes a hat-trick of midfielders ruled out of Tuesday night's clash having picked up his fifth yellow card of the season at London Road.
Winger Paris Cowan-Hall remains out with a groin injury picked up playing for the U21s against Coventry City in September.
Shane Ferguson (Northern Ireland) and David Forde (Republic of Ireland) are both unavailable due to international call-ups, although right-back Shaun Cummings is eligible to play for The Lions before he flies out to join up with the Jamaican national squad for their friendly against South Korea on 13th October.
Boss Harris welcomes back Sid Nelson from a rib injury that has seen the defender miss Millwall's last five games, whilst Joe Martin offers another option at the back.
With 75 per cent of Millwall's first choice midfield ruled out, the likes of Ben Thompson, Lee Martin, Jack Powell will all be hoping to be involved at some stage.
Wilder is also optimistic that a couple of other players may be back in contention after injury. Winger Alfie Potter could be in the squad having missed two matches with a dead leg, whilst defenders Brendan Moloney and Evan Horwood are now in full training.
However, Rod McDonald, Ricky Holmes and Paul Corry are still injured and will sit out the Second Round tie.
Head to head
The last time the two sides met was back in March 2009 when, in a season that was to end with The Lions reaching the League One Play-Off Final, a first-half goal from Gary Alexander secured a 1-0 home win for Kenny Jackett's side.