Midfielder James McCarthy made no excuses after Crystal Palace lost 2-0 to Southampton on Tuesday.
The Eagles' five-match unbeaten run in the Premier League was halted after goals from Nathan Redmond and Stuart Armstrong handed the visitors all three points.
Roy Hodgson's side had held champions Manchester City to a draw days earlier, but dropped two places to 11th in the table after this result.
"Each and every one of us know it's not good enough," McCarthy said. "We've got a lot of injuries in the squad but there's no point making excuses. As a squad, as a team, we know we're a lot better than that."
Palace now have a 10-day break until they return to action for the visit of Sheffield United on February 1.
The transfer window will be shut by then and, despite boss Hodgson repeatedly calling for additions earlier in the season, this week he has focused on players returning from injury.
Left-back Patrick Van Aanholt should be fit for the clash with the Blades after a hamstring issue and Andros Townsend and Christian Benteke will not be far behind.