Mayo, who was one of StarMine's top stock pickers in 2013, has a price target of $107 and a "buy" rating on Citigroup shares.
Citigroup reported quarterly earnings Oct. 14 but adjusted its net income Thursday to $2.8 billion from $3.4 billion, lowering earnings per share to 88 cents from $1.07, on legal costs.
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Mayo downplayed the amount of the earnings adjustment and said that Citigroup needed to show stability.
"They need to have day after day after day that's uneventful," he said. "Citigroup needs to become boring. Having said that, this is not life-threatening. The hit to book value is one-third of 1 percent, and Citigroup remains, what I think, the best restructuring story among global banks."
Mayo acknowledged Citigroup's past problems.
"I know as well as anybody, Citigroup would've effectively failed five times in the last century. They were the worst. They were the poster child for the problems during the recent financial crisis," he said. "My only book that I wrote, two of the 10 chapters are about how bad Citigroup is. Having said that, I think directionally they're going to the right place."
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Mayo also noted that Citigroup was simplifying its businesses, streamlining and cutting expenses—all ahead of a bleak outlook for financials.
"Citigroup's not relying on very aggressive revenue growth, and that's a good thing," he said. "We continue to think the U.S. banking industry will have the worst revenue growth this decade since the decade of the Great Depression. To put it in context, loan growth in the banking industry would normally have growth six times faster during this expansion than it's actually growing. So, I like the fact that Citigroup's not shooting for crazy revenue growth, which means they have less chance to blow up."
On Thursday, Steve Grasso of Stuart Frankel said that he wasn't a believer in the Citigroup story, preferring to buy Wells Fargo stock on a selloff.
"If you see a selloff in that, this is not going to be the same picture as a Citi," he said. "I would take advantage of that and buy that on a dip and stay away from a Citi, stay away from a Bank of America."
Brian Kelly of Brian Kelly Capital said Thursday that he would avoid the financials altogether.
"I, personally, do not want to be in any of the banks, but that's based on what the yield curve is doing," he said. "The yield curve is starting to flatten, and that's not good for banks."
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Disclosure: Mayo, a household member or an associate has a financial interest in the securities or related securities of Citigroup. Grasso does not own Wells Fargo, Bank of America or Citigroup. Kelly does not own Citi.