Interim manager Alan Curtis was disappointed with Swansea City's FA Cup exit but does not think it will affect their Premier League survival bid.
Swansea, 17th in the Premier League, host Sunderland on Wednesday.
"It's a huge setback to the club [but] I don't think it will impact [the game] on Wednesday and the rest of the Premier League," Curtis said.
"We were very disappointing and we're going to have to lift everybody for Wednesday but I'm sure that won't be a problem.
"We realise it's a massive game and we're going to have to play a lot better."
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Swansea are two points clear of the relegation zone and four points ahead of next opponents Sunderland, who are 19th. The visit of the Black Cats is the first of four home games in their next six league fixtures.
Jefferson Montero's sublime strike gave Swansea the lead at Oxford before Liam Sercombe levelled from the penalty spot.
Kemar Roofe's two goals put Oxford in control with Bafetimbi Gomis' strike a consolation for the visitors.
Curtis made 10 changes for the third-round tie at the Kassam Stadium but insisted they did not underestimate Michael Appleton's team.
"I thought the team that we picked was strong enough to have got the result," Curtis added.
"All credit to Oxford, they were certainly the better team. We knew they were a good side.
"The only time we really looked like a Swansea City team is when we were 3-1 down.
"We kept the ball a lot better and started to create a few chances but it was far too late then."
|Six key Premier League fixtures in a month|
|Swansea v Sunderland (13 January)||Swansea v Watford (18 January)|
|Everton v Swansea (24 January)||West Brom v Swansea (2 February)|
|Swansea v Crystal Palace (6 February)||Swansea Southampton (13 February)|