By Oliver Hirt

ZURICH (Reuters) -A preliminary investigation by Credit Suisse (SIX:CSGN) found that its Chairman Antonio Horta-Osorio attended the Wimbledon tennis finals in July during a visit to Britain when the country's COVID-19 rules required him to be in quarantine, two sources familiar with the matter told Reuters.

It's the second time the Portuguese banker, who joined the Swiss bank in April to clean up its culture following a string of scandals, has been found to have broken coronavirus curbs.

The findings of the investigation by Credit Suisse's legal team were passed to the audit committee on the bank's board before Christmas. It will now investigate and decide whether any further action needs to be taken, the sources said.

Spokespeople for Credit Suisse and Horta-Osorio declined to comment when asked about the investigation and its findings.

Horta-Osorio admitted to breaching Switzerland's COVID-19 rules during a visit to the country on Nov. 28. Swiss rules stipulated that he should spend 10 days in quarantine upon arrival but he left the country again on Dec. 1.

Reports of the Swiss breach prompted the bank's board to commission the internal investigation.

In the course of their investigation, the bank's legal team found that Horta-Osorio had also broken Britain's rules when he made the trip to attend Wimbledon for the finals on the weekend of July 10 and 11, the sources said.

At the time, Switzerland and most other European countries were on Britain's "amber list", which meant visitors had to quarantine for 10 days when they arrived in the country.

A UK government spokesperson said they would not comment on specific cases.

"Passengers are responsible for ensuring they comply with all travel rules, including providing accurate information on their Passenger Locator Form, and failure to do so could lead to a fine or imprisonment," the spokesperson said.

Horta-Osorio's Swiss breach is being reviewed by prosecutors in the canton of St Gallen after he reported it to them and he could face a fine of up to 5000 Swiss francs ($5,450).

($1 = 0.9172 Swiss francs)