Slaven Bilic admitted West Ham are fighting for Premier League survival following a 3-0 defeat to Arsenal at Emirates Stadium on Wednesday.
The loss was West Ham's fifth in succession, while they are now seven winless since a 3-1 victory at Southampton over two months ago.
Bilic was earlier this week given the backing of the club's board, who insisted his position was not under threat despite a string of disappointing results.
West Ham are now just five points clear of the relegation zone, but the Croatian is confident one win will be enough to get them back on track.
"Of course we are [in a relegation battle]. We don't have to hide it. It's not being negative, it's being realistic," Bilic told BBC Sport.
"I told the players to forget today - we have big games ahead of us. It's a massive game against Swansea on Saturday. We are in a fight to keep our Premier League status. We have to start winning games.
"To get that confidence back is the key point. One win will change everything for us, because three points at this stage of the season are massive."
Bilic was pleased with his side's display in the first 45 minutes, but felt a change in tempo from Arsenal after the restart was key to their downfall - Mesut Ozil, Theo Walcott and Olivier Giroud all scored in the second half.
"Arsenal deserved to win. The first half was okay, not only because of the score but we were good. We defended well with numbers. And we were also good on counter-attacks," said Bilic.
"In the second half they raised the tempo and scored a goal, and they were the better team. They were sharper than us.
"We wanted to keep a clean sheet and the draw as long as possible, or even better to score, and make their fans and players a bit more nervous. But they started to play with more freedom after scoring."