Manchester United midfielder Ander Herrera has told United Review he feels he can offer "more and more" to the team but "cannot sleep" if he is to keep his place.
Herrera, 27, inspired Jose Mourinho's side to a 2-0 win over Premier League leaders Chelsea at Old Trafford on Sunday, setting up Marcus Rashford's opener before adding the second with a deflected shot.
He said he wanted to keep pushing himself to improve as United fight for the Europa League trophy and a top-four finish and added: "Now we are in the crucial moment.
"Nobody will remember this part of the season if I don't perform well at the end. I am happy, but I am not finished yet.
"I like to demand a lot of myself because I feel I can give more and more and more to the team.
"I am happy, and I think it is the right attitude. So far it has been OK for me, but I still have to show I can give more.
"I am a team player, I want to give everything for the manager and I don't look back. I just look forward. The next month and a half is the most important time of my career."
Herrera said that he did not believe too much praise "is good for yourself, so I don't listen too much," adding: "I want to be focused on what is coming. I want to play in the Champions League next season."
He added that United boss Mourinho "gave me, from the first day, a lot of confidence and he told me I was going to be an important player for him."
"I will always be thankful, but football changes," he said. "We have great players and Manchester United has the capacity to sign big players so I cannot sleep.
"I have to keep working, performing and giving what the manager wants me to give."