Speaking after his side's 4-1 pre-season friendly win over Accrington Stanley, Martinez hinted that more signings may follow.
"I think it is important to bring in players early. I do feel the squad has always been strong and we have got great experience, but we needed to have certain additions to have different options," he told the club's official website.
"You can never stop searching, you can never stop looking to help the players that we've got at the football club.
"I can imagine the next four weeks are going to very much be about assessing the competition that we've got in the squad, assessing the youngsters and how quickly they can help and how quickly they can be prepared to have a role in the first team. Then we'll always keep an eye to try to be as strong as we can be at the start of the season."
Roberto Martinez began his managerial career at Swansea City, before moving to Wigan and winning the FA Cup in his fourth and final season with the club.