Tom Sizemore was never supposed to be in this film at all. As we already know, Billy Bob Thornton had his part, and only dropped out because he physically couldn't do the beach scenes that were required of him. That opened the door for Sizemore, but Sizemore was a man who was already fighting battles of his own.
Sizemore had a serious drug problem; one that plagued him both before and after the making of 'Saving Private Ryan', but not during. Spielberg warned him when he was hired that he'd be blood tested every single day during filming, and if he failed once, he'd immediately be fired from the cast, and his role would be re-shot by a replacement. Sizemore's part required 58 days of filming; replacing him would mean a lot of additional work both for Spielberg and for all the other actors involved in shooting his scenes. Thankfully - for this time, at least - Sizemore was able to stay clean.