Old filling came out leaving a hole in back molar, can it be re filled or a crown put on?

Years ago had two cavities near the gumline on the top right and left back molar filled and were done badly. The left one came out yesterday while brushing, leaving a good size hole from the gumline about halfway down the tooth, and bout halfway deep. It's brown stained from stuff building up behind it. Other than that there's no pain and the tooth isnt loose at all. What will probably be the best solution? Can it be re filled or a crown put on without a root canal? I have an appt Tuesday luckily.