Fulham's players did not battle hard enough to keep the club in the Premier League, says manager Felix Magath.
The Cottagers were relegated following a 4-1 defeat at Stoke coupled with Sunderland's win at Manchester United.
"There was no reason for that performance - it's the worst game since I've been here," said the German, who replaced Rene Meulensteen in February.
"You can never say any player would like to see relegation, but they didn't fight enough, especially today."
The west London club complete their season at home to Crystal Palace next Sunday, before they return to the second tier of English football for the first time in 13 years.
The Cottagers have lost more matches this season than any other team in the Premier League - 24 - and have the worst defence having conceded 83 goals, 11 more than bottom club Cardiff.
They were rock bottom when Magath was brought in by new owner Shahid Khan with 12 games to go.
The 60-year-old, who won three league titles with Bayern Munich and Wolfsburg, was the club's third manager of the season, following Martin Jol and Meulensteen.
The club's form slowly improved and they recorded back-to-back wins against Aston Villa and Norwich in April. However, Fulham were back in the mire when a heavy defeat against Tottenham was followed by a 2-2 draw against Hull last week - where they let a two-goal lead slip.
At the Britannia Stadium on Saturday, they were undone by strikes from Peter Odemwingie, Marko Arnautovic, Oussama Assaidi and Jon Walters. Kieran Richardson grabbed Fulham's consolation - which was only their second of two efforts on target.
"At the end, it [the recent performances] was better than before but not good enough," said Magath.
"Regarding today, the only thing I can imagine was there was too much pressure for the players.
"I didn't expect it. We were fighting against relegation. I told the team, today was a great chance but we never took the chance."
He added: "I've never been relegated until today. I feel very sad. I have to apologise for not managing the situation. The club asked me to come - I tried."
Magath signed an 18-month contract with the club and expects to lead the team in the Championship.
"I like it at Fulham, the club and the English way of playing football. I want to build a new team - that was the idea when I came here," he said.
Meanwhile, Stoke boss Mark Hughes said he was delighted with his side's level of performance.
"It was a difficult game for us because it was deemed a game we didn't have anything to play for but we knew what we wanted to achieve today and that was three points," he said.
"We made it difficult for Fulham once we scored that first goal which was really important. It might have been more difficult if they had got in front but they had to throw people forward to get on level terms and that played into our hands."