Altice co-founder Patrick Drahi has told investors he feels "betrayed" amid an ongoing corruption probe taking place in Portugal that has shaken the company in recent weeks.

French billionaire Drahi said the probe into fellow co-founder and former chief operating officer Armando Pereira has "shocked" him.

Pereira has been placed under house arrest in Portugal since last month, on the order of a judge as public prosecutors investigate corruption allegations.

Since the probe started, 15 employees have been placed on leave in Portugal, France, and the United States, said Drahi. Despite this, the scope of the probe is currently limited to Portugal.

"This has come as a shock and as a huge disappointment to me," Drahi said in a call in his first public comments on the probe.

"If these allegations are true, I feel betrayed and deceived by a small group of individuals, including one of our oldest colleagues."

Pereira, who was regarded as Drahi's most trusted lieutenant, has denied any wrongdoing. Drahi maintains that Pereira has not held any stake in any Altice entity since 2005.

As reported by the Financial Times last month, the investigation centers around Pereira and businessman Hernâni Vaz Antunes, who is also under house arrest.

It's alleged that both were involved in a scheme to rig the French group’s local procurement processes in Portugal.

Altice has opened its own internal investigation, suspending some employees, and said it's cooperating with the investigators.

Prosecutors in the country suspect that procurement decisions taken at Altice were rigged in a way that harmed the group’s own companies and competitors and benefited intermediaries.

Portugal's Central Department of Criminal Investigation and Prosecution noted that documents considered relevant for proving the alleged offenses have been seized as part of the investigation, plus objects representative of the result thereof, such as luxury vehicles and exclusive models with an estimated value of around €20 million ($22m).

"It is very unpleasant to see the word corruption next to the name of our group and most of the time in press articles next to my name," added Drahi.