But Blatter - who is meeting top Brazilian officials next week to discuss progress - was also confident Brazil would be ready to host the 32-team tournament despite the challenges.
Brazil is struggling to build the infrastructure needed for the World Cup and the eight-team 2013 Confederations Cup curtain raiser. In March, FIFA's general secretary said Brazil needed a "kick up the backside" to speed up the work.
Blatter apologised for the remarks by Jerome Valcke but still has some concerns about the pace of construction.
"Somewhere there are some delays and what we are doing now is to make sure that what has not been (done) in the past will be done as soon as possible and not later," Blatter told reporters, speaking in English.
"For the time being we are a little bit concerned about some constructions. But you know, constructions, if you push them and to put a lot of energy behind, then you can be ready on time," he said after an Ottawa event to mark the 2015 women's soccer World Cup, which Canada is hosting.
Next week Blatter will hold two days of meetings in Zurich with Brazilian Sports Minister Aldo Rebelo and the local organizing committee.
The FIFA chief noted that South Africa had successfully held the 2010 World Cup despite widespread doubts ahead of time that it would be ready.
"We are confident, because Brazil is not only a footballing nation but Brazil is also a very important economic power ... So I'm sure that they will do it," he said.
Blatter also reiterated that he wanted goal-line technology to be used at the Confederations Cup and the World Cup.
FIFA is currently testing two systems designed to determine whether a ball has fully crossed the line or not.
World soccer's governing body was embarrassed during the 2010 World Cup when a shot by England's Frank Lampard against Germany crossed the line but no goal was given.
"I can tell you FIFA in the World Cup 2014, and therefore already in our Confederations Cup in 2013, we will use this system. We cannot repeat the ... same situation we have witnessed in the match between England and Germany," Blatter said.
But he ruled out using any other kind of technology in the game. Some are calling for video replays to be used in a bid to eradicate officiating errors.
"Otherwise the game will lose its human face and there will be no more discussion if everything is perfect. Our game is not perfect and that's why it is ... so popular," he said.