It would also damage the image that the Brotherhood itself promoted for the past year, insisting it does not seek a theocracy in Egypt or to quickly implement Shariah.
El-Shater, a strongman in the Brotherhood, is pushing heavily to prevent a split in the Islamist vote in the May 23-24 vote to elect the first president since Mubarak's ouster. A single Islamist candidate could enjoy a widespread popular base, since the Brotherhood and Salafis together won more than 70 percent of parliament in elections late last year.
The Brotherhood alone holds nearly half of parliament and, alongside Salafis, dominates a new commission formed to write a new constitution. It is hoping for the presidency to seal its power.
But there are multiple candidates running on their Islamic agenda, dividing the vote and raising a possible window of victory for a non-Islamist figure.
El-Shater faces tough competition from a lawyer-turned-TV preacher, Hazem Abu Ismail, who is the favorite of Salafis. Abu Ismail has become ubiquitous in the campaign, plastering what seems like every other lightpost and wall in Cairo with campaign posters showing his cheerfully smiling face and long, conservative beard. After el-Shater announced his candidacy over the weekend, Abu Ismail rejected pressure to quit the race and many prominent Salafis announced they were sticking with him.
"There is grave fragmentation among ranks of Islamists and its getting worse with strong polarization between the two camps of candidates," Khaled Said, a Salafi leader, said.
Salafis are the most hard-line of Egypt's fundamentalists, depicting themselves as the "guardians of Shariah" and touting a strict interpretation of Islamic law similar to Saudi Arabia's. Many of them see the Brotherhood as too willing to compromise on implementing Shariah and despise its political pragmatism.
Leading clerics with their trademark long, bushy beards and robes have become regular guests on TV talk shows and issue fatwas or religious edicts attacking secularists, saying Christians and women can't run for president, and calling for greater segregation of the sexes.
El-Shater met for four hours Tuesday night with a panel of Salafi scholars and clerics, called the Jurisprudence Commission for Rights and Reform, trying to win their support.
The discussion focused on "the shape of the state and the implementation of Shariah," the commission said on its Facebook page Wednesday.
"El-Shater stressed that Shariah is his top and final goal and that he would work on forming a group of religious scholars to help parliament achieve this goal," the statement read. The commission is an umbrella group of Islamist factions, mostly Salafis, set up after last year's anti-Mubarak uprising.
A Brotherhood spokesman could not immediately confirm the offer and attempts to reach the head of the commission went unsuccessful.
The promise resembled an item in a 2007 political platform by the Brotherhood, when it was still a banned opposition movement. It called for parliament to consult with a body of clerics on legislation to ensure it aligns with Shariah. The proposal was met with a storm of condemnation at the time, and the Brotherhood backed off of it.
Mohammed Habib, who was the Brotherhood's deputy leader at that time, says the platform item was for a body of clerics simply to advise lawmakers, but that some in the group wanted it to have a more powerful role to vet legislation.
Of el-Shater's reported proposal, he said there were many questions. "Does it cut powers from parliament? Would it have the power to impose anything on parliament?" he said, speaking to the Associated Press.
Tharwat el-Kherbawi, a former Brotherhood member who fell out with the group, said the council appeared similar to Iran's system of clerical "guardians" over the elected government.
"El-Shater wants to give Salafi clerics what they want," he said. "The clerics will work on moving the Salafi mountain from Abu Ismail to el-Shater but first they need some melting of the ice. And this is the way to get through it."
The Brotherhood announced el-Shater's nomination over the weekend, breaking a yearlong promise that it would not run a candidate for the presidency. The move raised accusations that the Brotherhood is trying to monopolize all levers of power. It also angered many Salafis because it would split the Islamist vote.
Another Islamist candidate in the race is Abdel-Moneim Abol-Fotouh, a longtime Brotherhood member from its reformist wing who was booted out of the organization last year when he announced he would run for president. His campaign has drawn support from young, reform-members of the Brotherhood.
El-Shater has held multiple meetings with Salafis trying to win support and pressure Abu Ismail to drop out, said Salafi cleric Amin el-Ansari, who is close to Abu Ismail's campaign.
Some Salafis do see an appeal in el-Shater because the Brotherhoods' more disciplined organization could be more likely to bring results, el-Ansari said.
"This is reassuring to the clerics and to the voters," he said. "The Muslim Brotherhood members are like cogs in a machine and like soldiers who wouldn't violate the decisions of their leadership."
So far, however, Abu Ismail is staying in the race.
In a meeting in the Mediterranean city and Salafi stronghold Alexandria, Abu Ismail was asked to withdraw. He refused, replying, "the one who created sedition is the one who should put it down," in reference to el-Shater's nomination, according to his aide Gamal Saber.
Saber also threatened that unless the Al-Nour party, the Salafi's main political arm, endorses Abu Ismail, hundreds of young party members would break away.
Abu Ismail faces a possible hitch. Opponents are demanding an investigation into reports that his mother holds American citizenship. If true, it would disqualify him from the race, since the rule bar any candidate with a foreign parent. Abu Ismail has insisted his mother is not a U.S. citizen.