Fourteenth-placed Everton have shipped 17 goals after seven matches in all competitions this season, the most since the 1994-95 campaign when Mike Walker's side let in 18 goals after seven games.
The same backline conceded 39 goals in the Premier League last season and the Everton boss believes it is only a matter of time before his side are a defensive force once again.
"We haven't made any major changes in those places of the team. The focus as a team to defend has to be better," Martinez told a news conference on Thursday.
"It's clearly an area that we need to resolve in the coming weeks. The performances have got better."
Everton have not won a Merseyside derby in four years, but Martinez has reason for optimism as fierce rivals Liverpool have also started the season in lacklustre fashion, managing six points from their first five games.
Martinez's side head to Anfield on the back of a 3-2 loss to Crystal Palace - an exact repeat of the victory the south Londoners managed at Goodison Park in April.
"The defeat against Crystal Palace, there was something spooky about it," Martinez added.
"The last time we beat Liverpool at Anfield was Sept. 27 so I hope the spookiness carries on at the weekend.
"It's very important at this stage of the season to get the moments of form to the players, to make sure we become as strong as we can be.
"The game at the weekend will test us to the maximum. It's going to be a really good occasion and one of the most exciting games of this campaign.
"It's still only three points but three points are becoming very important for both sides after we dropped points. It's really important to start getting a consistent run of results."
Everton will hand late fitness tests to defender Seamus Coleman and midfielder Steven Pienaar, while England midfielder Ross Barkley is making steady progress in his recovery from a knee ligament injury.
"Steven Pienaar is recovering really well and we are going to assess him over the next few days," added Martinez.
"It's the same with Seamus. Both are in the same situation where it is too early to tell if they are going to be fit for the weekend.
"Ross Barkley is recovering quicker than we thought but it is still in the early stages. We can't rush it. Even when you feel right, medicine always wants one day more."
(Reporting by Michael Hann, editing by Ed Osmond)
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