The chairman of Credit Suisse, António Horta-Osório, has resigned after the Swiss bank found that he had broken Covid-19 quarantine laws, with attendance at the Wimbledon tennis tournament thought to be among the allegations.

Horta-Osório, the former chief executive of Lloyds Banking Group, said in a statement that his “personal actions” had made it more difficult for him to represent the bank. He had also admitted breaking Swiss quarantine rules.

It means that Horta-Osório managed less than a year in the job, after he was brought in to steady the bank after a series of expensive failures, including its involvement in the collapse of Archegos, an investment company, and Greensill Capital, a supply chain finance firm.

“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-Osório said in a statement issued by Credit Suisse on Monday.

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

The board held talks with Horta-Osório over the weekend informing him of the findings of its investigations into a series of alleged breaches of Covid-19 rules, according to a person briefed on the issue. It is understood that Horta-Osório decided his position would be untenable after being informed of the findings.

The alleged UK breach emerged in December, after Reuters reported it had been discovered through a preliminary investigation by Credit Suisse’s legal team. The news came just weeks after Horta-Osório admitted that he had breached Covid rules in Switzerland, having flown out of the country within three days of arriving on 28 November despite being required to quarantine for 10 days.

The alleged Swiss breaches were first reported in the national press. Swiss newspapers also alleged that Horta-Osório had consulted a senior politician to try to secure an exemption from rules, despite his apology later describing his error as “unintentional”.

Credit Suisse confirmed on Monday that Horta-Osório had resigned after an investigation commissioned by the board but did not give any details of the findings.

The bank has appointed Axel Lehmann, formerly a senior executive at its Swiss rival UBS and the Swiss insurer Zurich, to take over as chair of its board.

Lehmann said the bank had “set the right course with the new strategy” that Horta-Osório had overseen, and added it would carry it out in a “timely and disciplined manner, without distraction”.

Horta-Osório attended the Wimbledon tennis tournament on 10 and 11 July 2021, having flown to the UK from Switzerland. At that time Switzerland was on the UK government’s amber list of countries that required arrivals to isolate for 10 days.

Breaching quarantine rules was a criminal offence, according to UK government guidance, which stated that police could issue offenders with fines starting at £1,000 and rising to £10,000 for repeat offences.

The Portuguese executive had been brought in by Lloyds in 2010 as chief executive after the bank’s government bailout during the financial crisis. The government sold its last remaining shares in May 2017 under his watch, but Horta-Osório had already drawn criticism for large bonus payments.

Lloyds announced his departure in 2020, and Credit Suisse reported his appointment six months later. Horta-Osório was brought in to steady the ship after the bank admitted hiring private detectives to spy on executives. Just as he was due to start in the role, Credit Suisse’s prime broking arm was hit by a loss of £3.4bn related to Archegos, a previously little known hedge fund that borrowed from banks to make a series of disastrous bets. It was swiftly followed by the collapse of Greensill Capital, a supply chain finance fund run by Australian banker Lex Greensill.

Horta-Osório had been tasked with overseeing a strategy relaunch, including a clearer focus on managing the risks posed by clients. He had also worked with the Credit Suisse chief executive, Thomas Gottstein, on replacing several senior managers.