Blatter gave his support to comments from anti-corruption lawyer Mark Pieth, who worked with FIFA on potential reforms when Blatter was boss, saying fans should stay away from the USA for the tournament.
"I think Mark Pieth is right to question this World Cup," Blatter said on social media.
Pieth cited the killing of protester Renee Good by an American immigration agent in Minneapolis earlier in January as one reason for supporters not to travel to the USA, with Blatter's endorsement of his comments coming in the wake of the death of a second US citizen, Alex Pretti, last weekend.
The World Cup is due to be hosted by the United States, Canada and Mexico from June 11 to July 19.
"What we are seeing domestically - the marginalisation of political opponents, abuses by immigration services, etc. - hardly encourages fans to go there," Pieth said in an interview with Swiss daily Tages-Anzeiger last week.
"For fans, just one piece of advice: avoid the United States! You'll get a better view on television anyway.
"Upon arrival, fans should expect that if they don't behave properly with the authorities, they will be immediately sent home. If they're lucky..."
Blatter stepped down as FIFA president in 2015 amid several scandals and was replaced by current boss Gianni Infantino.
Blatter and former UEFA chief Michel Platini were last year acquitted definitively on charges stemming from a delayed payment of two million Swiss francs (£1.8 million) that FIFA made to Platini in 2011 for consultancy services.
Former France star Platini said earlier this month that Infantino, who has forged a close relationship with US President Donald Trump, has "become more of an autocrat" and "he likes the rich and powerful".