The Toffees lost 2-1 at Norwich on Saturday following a late rally by the home team in a match they should have long put to bed after taking a first-half lead through Leon Osman.
Moyes' men have now not won in the Barclays Premier League in three attempts, which has seen them fall six points behind Tottenham, who have played a match less, in the race to finish in the top four.
Everton host Oldham in a FA Cup fifth-round replay on Tuesday night as they aim to move into the quarter-finals, where they would be at home to Wigan.
Naismith insists the first-team group - one of the smallest in the Premier League - just have to roll their sleeves up and get on with it.
He said: "The squad haven't moaned about tiredness, it is not something we've spoken about.
"We're professionals and you have to go out and do your job. We work every day and we work at a good level so the boys are definitely fit enough. I don't think they're tired at all."
- Sports & Recreation
- Barclays Premier League