Derby County lacked heart in the defeat against bottom-of-the-table Burton Albion and risk being torn apart if they do not improve, said centre-half Curtis Davies.
The Rams dropped out of the play-off places to seventh in the Championship table after Saturday’s 3-1 loss.
But they will go fifth if they win the game in hand they have on fifth-placed Middlesbrough and Millwall, in sixth.
Davies told BBC Sport losing to Burton was a “massive backwards step”.
“It was nothing to do with quality or ability, it was probably heart and desire and we lacked massively with that,” the 33-year-old added.
“We didn’t deserve to get anything out of the game.”
Derby dropped out of the top six for the first time in 144 days and now face successive games against promotion rivals Middlesborough, Cardiff and Aston Villa.
“We are playing our direct opponents,” said the ex West Brom, Villa, Birmingham and Hull City defender.
“If we play anything like we did against Burton, teams with the quality of Middlesbrough, Cardiff and Aston Villa will tear us apart. It’s not good enough.”
“It was always going to be a big week but now it’s make or break.”
Derby have won just five of their 17 league matches in 2018, with boss Gary Rowett describing the recent home defeat against Sunderland as “probably the worst 90 minutes” in his time as a manager.
But Davies said the squad has to “stick together”.
“We need a reaction,” he said.
“We will have no excuses about pitches, quality of football and style. We just have to go out and do a number on someone.
“We played against Preston and it was an ugly game, a horrible game of football but we won 1-0. Against Bolton it was pretty comfortable so we never really had to work too hard to get going.”