The London club are guaranteed to end the season in the bottom three, together with Cardiff City, after being thumped 4-1 by Stoke City on the same day that fourth-bottom Sunderland won 1-0 at Manchester United.
Fulham delivered a woeful display at the Britannia Stadium and could have few complaints as a side managed by their former boss Mark Hughes romped to an emphatic triumph.
Magath, who arrived at Craven Cottage in February, apologised for failing to guide Fulham to survival, but struggled to explain his side's poor performance against Stoke.
"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," the experienced German is quoted as saying by BBC Sport.
"At the end it (the level of performance since his arrival) was better than before, but not good enough. Regarding today, the only thing I can imagine is there was too much pressure for the players.
"There was no reason for that performance - it's the worst game since I've been here. 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.
"The thing is you can never say any player would like to see relegation, but they didn't fight enough, especially today."
Fulham must now prepare for life in the Championship and Magath hinted that he is keen to stay at the club.
"It's hard for everybody who likes Fulham. I like it at Fulham, the club and the English way of playing football," he added.
"I want to build a new team - that was the idea when I came here."
