The teachers at UA would spring into action. Recovery Girl would start her healing process right away. Mr. Aizawa would be concerned about how this would affect Izuku's future as a hero. He might adjust the training regime for Izuku once he recovers to make sure this doesn't happen again. And the other students would be sending get - well - soon messages and visiting Izuku in the hospital.
His friends like Ochaco and Iida would likely be very worried. Ochaco might use her quirk to try and gently float Izuku to safety if possible, while Iida would be all about getting him medical attention as quickly as possible.
All Might would probably feel a sense of guilt, especially if he thinks he didn't train Izuku well enough. He might visit Izuku in the hospital and give him an inspiring speech to help him recover. Bakugo, on the other hand, might seem angry on the outside but deep down be worried. He could be seen pacing outside Izuku's hospital room, muttering about how Deku should have been more careful.