What is the ruling of Islamic law regarding a person afflicted with a knee injury refraining from praying on a chair with the Muslim congregation, despite the doctor's advice to do so?

Scholars have stipulated that the fear of increased illness or delayed recovery permits abandoning standing in prayer. If a trustworthy doctor informs a patient that sitting and prostrating are harmful to him, he may omit them and pray sitting on a chair during bowing and prostration, making his prostration lower than his bowing, while noting that it is not permissible to miss congregational prayer.