Calvert-Lewin scored 13 league goals in the 2019/2020 season and upped that tally to 16 the following campaign.
Another strong start to this season saw him notch three goals in his first three games but got sidelined for four months with a series of muscle injuries.
The 24-year-old is yet to score in five games since his return at the start of the year and has let out his frustrations.
“The injury was so frustrating because I started the season so well and I was in a good moment," Calvert-Lewin told Everton's official website.
“To re-injure the same leg three times, it was soul-destroying at points, and it takes you to the depths of a mental battle.
“It’s difficult seeing the boys play and you feel so far away. I’d feel close to coming back and then I was sidelined again.
“You have to dig deep and show courage and character. I feel I’m now a stronger person and a stronger player and off the back of that I’ll return to a top level.
“I’ve been training consistently for a couple of weeks. Now, I feel physically a lot better and much more confident in my body.
“I hold high standards for myself and when you’re not quite at that level that you expect, it can become frustrating.
“I’m trying not to get too frustrated with myself. The fitness and sharpness will come and I just need to keep getting in the right areas, doing the work, and I’m sure the goals will follow.”
