Hull (9-6-17) are 14th in the table on 33 points - level with Swansea but trailing the Swans on goal differential. Both sides are seven points clear of the drop zone and have six matches to play.
The Tigers won just one of their last five league matches despite playing some attractive football in recent weeks.
"We know it's in our hands," Harper told the Hull website. "We've got a big game on Saturday and we're looking forward to it. We know there is a lot of traffic below us, but we also know that if we don't get results then every weekend one or two below us will.
"We've got a clear week and we're fully focussed on Saturday, nobody is talking about anything else. Hopefully we can pack out the KC. In the last three games we've had one result (a 2-0 win against West Brom) and two decent performances (narrow loses against West Ham and Stoke), so hopefully we can put the two together on Saturday and get a good win."
Swansea (8-9-15) ended a run of six league matches without a win last Saturday when they beat Norwich City 3-0 at the Liberty Stadium. Jonathan de Guzman scored two first-half goals before Wayne Routledge added a third 15 minutes from time to secure all three points for the Welsh side.
Swans head coach Garry Monk was delighted with his team's performance against the Canaries but admits he is expecting a hard match when they travel north to Hull this weekend.
"It will be tough," Monk told the Swansea website. "But I also think it will be a good game. People will talk about their recent results, but overall they have had a good season. They have good, experienced players and we'll need to match their intensity and will to win the game.
"We realise the position we're in and we have still got a job to do. For me, I want a couple more wins to ensure we are safe. But I also want to win every single game, and if we can't then make sure we don't lose."
Hull will be without McGregor (kidney) and long-term absentees defender Paul McShane (ankle) and midfielder Robert Brady (groin).
Swansea defender Kyle Bartley is doubtful with a hamstring strain, but otherwise the Swans have reported no fresh injury concerns.
These sides drew 1-1 at the Liberty Stadium in Dec. 9 in this season's reverse league fixture. Hull striker Danny Graham scored against his old club to give the visitors the lead after nine minutes, before Swansea defender Chico Flores equalised from close range on the hour.