No. It's not the same. If Steve Young had been fired by the 49ers, because he refused to play on Sunday, he couldn't
claim "religious discrimination". It would have been a choice- a choice based on his desire to keep the Sabbath day holy- but a choice nevertheless.
Obviously, Steve didn't make that decision- and I'm glad he didn't. He's one of my favorite players ever. And he's also an incredible ambassador for the Church.