BARNSLEY will hope to win a ninth successive home league game in the same season for the first time in more than a century when they host lowly Oxford United from 3pm.
Oxford are currently 20th in the League One table, one point and one place above safety.
They are winless in their last 16 league matches since January.
This week they lost 1-0 at home to Bolton on Saturday and drew 1-1 at home to Portsmouth on Tuesday.
They sacked Karl Robinson during a run of one point from ten games and replaced him last month with Liam Manning who has drawn five and lost one.
Duff said: “They are a strange one.
“You look at their manager, club, budget and players, they are all really good and they should be much higher.
“Something has gone wrong, I am not sure what it is.
“I don’t need to know what it is.
“I just need to make sure they don’t get that bounce back against us.
“I have watched their last two games, they have shown a lot of spirit and had a right go.
“They have had 40-odd shots against two good teams in Bolton and Portsmouth.
“It shows they are not lying down.
“There might have been a period of ‘oh we will be alright’ and ‘we’re too good to go down’ but they are definitely past that now.
“They know they are in it and they have to scrap. We have to match their determination.
“We believe we can run harder than anyone else and hopefully that gets the fans going.
“It’s more complicated than against other teams down there because, when we have matched the determination of Morecambe and Accrington, without being disrespectful, we’ve been better than them.
“Oxford have some really good players.
“(Marcus) McGuane, (Cameron) Brannagan, Marcus Browne – they are top top players.
“They will be low on confidence, so we need to get on the front foot early and kill any spirit they have.”
Barnsley won 2-1 at Oxford on February 1, going 2-0 up then being put under serious pressure late on.
The Us have since changed manager, bringing in Manning who was sacked by MK Dons in December.
Duff said: “It’s been a slight tweak from 4-3-3 to 4-2-3-1.
“Liam is a footballing manager, anyone who saw his MK Dons knows that.
“They won’t defend in a low block, they will play football like a top ten team.”
Barnsley will look for a ninth straight home league win which would be the first time they have done so in the same season in more than a century.
“We have enjoyed playing at home.
“We have had gritty ones like Shrewsbury and Cambridge when our backs were to the wall with ten men, we’ve played some free-flowing stuff and some high-tempo, high-pressing stuff.
“People will say you can’t win 11 out of 11 at home. Why not? We just have to give everything.”
Barnsley midfielder Herbie Kane spent last season on loan to Oxford.
Duff said: “Herbie knows them better than I do. He will tell the others about how good they are. He played with a lot of those players.”