Bypass

My relative has a triple bypass in a  few days but is currently being treated for a collapsed lung with pneumonia. I am worried about going into surgery with the body being weak.

[Cleveland Clinic]

Absolutely, and so you should be. He will benefit from recovering from this acute stressor before undergoing major open heart surgery. Any surgery performed under distressing conditions portends a much higher risk of complications, failure to recovery, and negative outcomes.
Provided that the surgery is elective ( that is he has not had a heart attack and that the following heart failure exacerbation was not misdiagnosed as pneumonia), he should wait at least two  weeks before the surgery. Let the surgeon know what has happened and I am sure he will concur.