Sheikh Salman's credentials to run FIFA were questioned by the head of the English Football Association on Monday ahead of next week's election.
The Asian Football Confederation president is a leading candidate to succeed Sepp Blatter but remains under scrutiny over his role in Bahrain's Arab Spring uprising in 2011.
Last week another candidate, Prince Ali of Jordan, publicly questioned whether Sheikh Salman protected Bahrain players who alleged abuses after pro-democracy protests.
Sheikh Salman, a member of Bahrain's royal family who was president of the Bahrain Football Association at the time, has strongly and repeatedly denied wrongdoing.
Later Monday, the sheikh was praised by former presidential hopeful Michel Platini.
Platini, the suspended UEFA president, said his own general secretary, Gianni Infantino, and Sheikh Salman were the two front-runners in the five-candidate election.
"There are two favorites," Platini said at FIFA after an appeal hearing against his eight-year ban. "I have two people I really like."
But English Football Association chairman Greg Dyke said there remains "an issue about Bahrain."
"No one denies that there were violations of human rights involving sportsmen and footballers that went on four years ago," Dyke told the BBC. "No one denies that. The denial is over whether or not he was involved.
"The question is: Does it matter whether or not he was involved, or is it the fact, can you have someone from Bahrain running world football, in charge of world football, given what happened there four years ago? I personally have my doubts."
Sheikh Salman has often said government issues are not the responsibility of sports leaders and accused critics of creating "nasty lies about something they want to use for their purpose."
England is yet to publicly back a candidate, but hosted a campaign event for UEFA General Secretary Gianni Infantino.
Salman and Infantino are competing against South African businessman Tokyo Sexwale, former FIFA official Jerome Champagne and Prince Ali.
Although Salman has the backing of the Asian and African confederation executive committees, Infantino has more public endorsements from individual federations who vote on Feb. 26.
Infantino has been backed so far by at least 65 of FIFA's 209 member nations.
"Gianni, he's a person I trained a little over these last few years. I explained to him certain things," said Platini, whose campaign was backed by Sheikh Salman before FIFA suspended then banned him. "Salman, my friend, who announced he supported me from the start.
"It's difficult to really choose between one and the other," Platini said. "It's a bit complicated."SHOW MORE