Rafael Benitez says he did not realise the "magnitude of the task" at Everton following his sacking on Sunday after less than seven months in charge.
Everton have won only one of their past 13 Premier League games and are 16th in the table, six points above the relegation places.
"We knew it wouldn't be easy," Benitez said following his departure.
"It was a big challenge, both emotionally and in terms of sport. My love for this city, for Merseyside and its people, made me accept this challenge, but it is only when you are inside that you realise the magnitude of the task.