The Swans were knocked out at the first hurdle, going down 2-1 at The Walkers Stadium on Saturday afternoon despite taking a one-goal lead through David Cotterill.
"It was a great strike from David Cotterill. We work hard to score goals from outside the box and it is something we need to do more often," Swans boss Sousa said after the match."
Sousa went on to explain why Leon Britton, Ashley Williams, Nathan Dyer, Andrea Orlandi and Federico Bessoniall had all missed the game against Nigel Pearson's side: "Today was the best 11 we could have put out.
Those we left out all had the flu.
"I'm down because I'm out of the cup. It's a prestigious competition and brings money into the club."