The match is the first of three ‘win or bust’ fixtures for Northants as they look to complete a remarkable turnaround and qualify for the quarter-finals.
The Steelbacks looked dead and buried after losing five out of five at the start of the competition, but four wins in the past five have given them a chance of qualification.
Northants, who beat Lightning by seven wickets a fortnight ago, currently sit in seventh place in the North Group, but a win at Old Trafford will lift them above their sixth-placed hosts, and could see them level on points with the top four.
They are currently just two points off that all important fourth place with three matches to play, but Cobb says his sole focus has to be on the trip to Manchester.
“Going into the game we should be confident with the way we are playing our cricket,” said the skipper, who will be without the services of the injured Adam Rossington.
“We did beat them last time and we need to keep being brave because we have no other option really than to win.
“The target is to go into the last game with a chance of qualifying, and to do that we need to win two from two, so we have to keep performing.
“We can’t switch off now, and I know it’s a cliche, but ultimately it is one game at a time for us because if we mess up once, then that could be the competition over.
"We have to stay focused on that next game, continue to play good cricket, and be brave.”
Lightning have been dealt a blow as they have lost fast bowler Saqib Mahmood and leg-spinner Matt Parkinson to England ODI duty against Pakistan, but Cobb is still expecting a very tough encounter.
“They are two big players for them, but any team that Lancashire put out you know they are going to be a strong side,” he said.
“You know they are well drilled, and you know they still have plenty of experienced players who have been very successful in the competition.
“But from our point of view, it does give us a bit of an extra boost.”
The Steelbacks have named a 14-man squad for the trip to the north west.
Following Friday night's Blast fixture, Northants travel to Cardiff for their final LV= Insurance County Championship Group 3 fixture against Glamorgan.
Steelbacks squad v Lancashire: Josh Cobb (c), Ben Curran, Brandon Glover, Freddie Heldreich, Rob Keogh, Richar Levi, Mohammad Nabi, Wayne Parnell, Ben Sanderson, Tom Taylor, Charlie Thurston, Ricardo Vasconcelos, Graeme White, Saif Zaib.
Lancashire squad: Dane Vilas (c), Finn Allen, Jack Blatherwick, Josh Bohannon, George Balderson, Steven Croft, Alex Davies, Tom Hartley, Liam Hurt, Keaton Jennings, Rob Jones, Danny Lamb, Jack Morley, Luke Wells, Luke Wood