Ronald Koeman's side travel to Bramall Lane for their quarter-final showdown having lost their previous four matches, the latest a 1-0 reverse at Burnley on Saturday.
One positive for Southampton in that match, however, was the return of Ward-Prowse following nearly two months out with an ankle injury.
The midfielder expects United to present a challenge not unlike Burnley and believes the Premier League side must earn the right to play against their League One opponents.
"It will be similar to [the game against Burnley]," Ward-Prowse told the club's official website.
"They'll want to battle and fight so we'll have to battle first and hope the technicality shines through.
"We know what's required and we're desperate to turn our form around and get back on track.”
Part of the reason for Southampton's strong form in the League Cup this season has been Koeman's tendency not to make wholesale changes to his side, which had done so well in the league until recently.
But Southampton must do without top scorer Graziano Pelle if they are to return to their early season performance levels on Tuesday. The Italian is suspended after picking up a fifth booking at Turf Moor.
United have lost just once in their previous seven matches, following Saturday's 1-1 draw at Fleetwood Town.
Midfielder Stefan Scougall missed that match through injury, but manager Nigel Clough expects to have more players to pick from on Tuesday, employed in a less expansive system.
"I don't think we'll go with the same system on Tuesday," Clough told Sky Sports.
"We had a few who weren't fit to start and few who didn't make the 18.
"We hope we're taking momentum into that game.
"We'll need everything we can get to deal with Southampton."
Southampton should approach their trip to Yorkshire with caution as United reached the FA Cup semi-finals last season, knocking out two Premier League sides in Aston Villa and Fulham on their way to Wembley, where they lost 5-3 to Hull City.
And Clough's men claimed another top-flight scalp in the second round of the 2014-15 League Cup by beating West Ham on penalties at Upton Park back in August.
Southampton, meanwhile, were victorious at both Arsenal and Stoke City to progress to the last eight.
