The head of Credit Suisse has resigned less than a year after taking the reins of the scandal-hit bank following reports that he had broken Covid quarantine rules.

Antonio Horta-Osorio's resignation was effective immediately following an investigation commissioned by the board, Switzerland's second-largest bank said in a statement released Monday.

Board of directors member Axel Lehmann was appointed to take his place.

"I regret that a number of my personal actions have led to difficulties for the bank and compromised my ability to represent the bank internally and externally," Horta-Osorio said in the statement.

"I therefore believe that my resignation is in the interest of the bank and its stakeholders at this crucial time."

Credit Suisse confirmed last month that Horta-Osorio had violated quarantine rules following a report by Swiss tabloid Blick.

Switzerland tightened conditions to enter or return to the country in late November following the emergence of the highly-contagious Omicron variant.

Blick reported in December that Horta-Osorio had travelled to Switzerland from Britain aboard a private jet after the UK was placed on a list of countries bound by quarantine rules.

After arriving at his home, Horta-Osorio asked if he could be released from isolation or if the measure could be shortened for him, the newspaper said.

Despite getting no answer from the authorities, the banker took the plane to the Iberian peninsula before heading to New York for a board meeting.

The resignation adds to the woes of the Swiss banking giant, which was rocked by its links to the multi-billion-dollar meltdowns at financial firms Greensill and Archegos last year.

Horta-Osorio, who built a solid reputation in having turned around British bank Lloyds, had pledged to tackle risk at Credit Suisse.

'Without distraction'

"We respect Antonio's decision (to resign) and owe him considerable thanks for his leadership in defining the new strategy, which we will continue to implement over the coming months and years," Severin Schwan, vice chair of Credit Suisse's board, said in the company statement.

"Axel Lehmann as the new Chairman, with his extensive international and Swiss industry experience, is ideally suited to drive forward the strategic and cultural transformation of the bank," he said.

The board will propose that Lehmann, who has headed the risk committee since October, take over permanently as chairman at the annual general meeting on April 29, the bank said.

"We have set the right course with the new strategy and will continue to embed a stronger risk culture across the firm," Lehmann said.

"By executing our strategic plan in a timely and disciplined manner, without distraction, I am convinced that Credit Suisse will demonstrate the renewed strength and business focus needed to generate sustainable value for all of our stakeholders," he said.