Fernandes was Ten Hag's captain at United, taking the armband from Harry Maguire at the beginning of last season.
"Whenever you see a manager go you have to take some of the blame on yourself. It is because the team is not doing so well," Fernandes told Sky Sports, after scoring in Sunday's 1-1 draw against Chelsea.
"It is easier to get rid of a manager than 15 players. I spoke to the manager and apologised to him, I was disappointed he has gone and I tried to help him.
"I wasn't scoring goals, we are not scoring goals and I feel responsible.
"I normally score a lot of goals but I always gave 100 per cent. He is aware of that."
Fernandes also scored twice in a 5-2 thrashing of Leicester in the Carabao Cup.
"In midweek the goals went in. I said to some friends everything will come to us and people will say we wanted the manager to be sacked," added Fernandes.
"We need to be disappointed because we are far back in the league."
However, Fernandes has welcomed the appointment of new manager Ruben Amorim from his former club Sporting CP.
"I am a big fan of Sporting and watch a lot of their games. Ruben Amorim brought the excitement back to the club," said Fernandes.
"He transformed everything and brought everyone together."