Swansea's match against Stoke next Saturday is probably the club's biggest since the 2011 Championship play-off final, says manager Paul Clement.
Saturday's 1-0 Premier League defeat at Watford leaves Clement's side two points behind 17th-placed Hull City with five games remaining.
Under Brendan Rodgers, the Swans won promotion to the top flight by beating Reading at Wembley in May 2011.
"With the position we are in, Stoke becomes a must-win game," said Clement.
"It is probably the biggest game the club has seen in a few years, probably since the play-off final."
Clement has previously been dismissive of the notion of "must-win" games.
"I've been asked a lot since I joined, 'is that a must-win game?' but there were still lots of games to play," he said.
"Now the next game is huge. We have to win, we have to beat Stoke. The players know that, what we need is to embrace this pressure.
"When the pressure is gone, we won't be able to stay in this league. So we have to continue to believe. We have three home games at the Liberty and with the fans' support, hopefully it will be enough."
|Swansea's remaining fixtures||Hull City's remaining fixtures|
|Stoke City (h)||Watford (h)|
|Manchester United (a)||Southampton (a)|
|Everton (h)||Sunderland (h)|
|Sunderland (a)||Crystal Palace (a)|
|West Brom (h)||Tottenham (h)|
'It's a confidence issue'
Chelsea legend Frank Lampard, who Clement tried to sign prior to his retirement, says Swansea's poor form is down to a lack of confidence.
"I understand if Paul Clement seemed downcast at full-time," he said. "It was disappointing from Swansea's perspective - the one thing you expect as a manager is effort and a desire to get out of the situation they are in.
"That was slightly lacking from the start. Swansea were short in their energy and what they put into the game.
"It's a confidence issue - they are on a bad run and gave sloppy balls away throughout the game.
"It looks like a straight fight now between Swansea and Hull for that last relegation position.
"I watched Hull today and they are a team creating chances. You can see that they have some momentum."
Mawson 'really upset'
Clement said defender Alfie Mawson was distraught after his mistake led to Etienne Capoue's winning goal for Watford.
"I hope Alfie Mawson would have learned after the last game, because he was taking some risks in that one," Clement said. "I said to him at half-time: 'That has to be it now.'
"He's a good player and he will learn from it. He's going to end up being a very good player, but his job is to keep it simple.
"Alfie is really upset, he knows he's made a big mistake."