Pope Francis apologized Wednesday for staying seated during his weekly audience, blaming a troublesome knee that has seen him cancel several engagements in recent days.

“I apologize because I will greet you sitting down, because this knee has not finished healing, and I cannot be on my feet for long,” he said after the audience in St Peter’s Square.

“Excuse me for this, thank you,” the 85-year-old told the assembled crowd, to applause. The Argentine pontiff had cleared his diary on Tuesday due to pain in his right knee, and also canceled engagements last Friday to undergo medical checks.

He appeared to have trouble walking due to the problem, which also saw him cancel some events in February and March, although he spent two days visiting the Mediterranean island nation of Malta as planned earlier this month. Pope Francis told Argentina’s La Nacion newspaper last week that he had a torn ligament in his knee, which he was treated by putting ice on it and taking some painkillers. He said he had been told it would go away in time, but the healing process “is slow at this age”.