New Delhi:Promising javelin thrower Neeraj Chopra, who scripted history by becoming the first Indian athlete to become a world champion at any level, said on Wednesday that a back injury had affected his preparations for the upcoming Rio Olympics, starting August 5. The Haryana youngster on Saturday won the gold medal at the under-20 World Championships in Bydgoszcz, Poland. Chopra threw a huge 86.48 metres to bag the gold but he did it after the qualification deadline of Olympics 2016 which was July 18. "I had a back injury in April and it affected preparation for the Olympics. In Poland, I had a targeted gold medal but I am happy that I eclipsed the world record, I had worked hard for it. My confidence was high for the event. But I never thought I will break the world record," Chopra told reporters on his arrival here. Chopra said he was disappointed to miss out on the Games this year but vowed to earn a gold medal for India at the 2020 Tokyo Olympics. The 18-year-old's coach Garry Calvert also heaped praises on his student. "He has a superior technique for his age and his whole character, he applies himself better than most. Now we have to go back to the drawing board and get more power and strength to match the men in the world," Calvert said. "We saw this threw coming for 6-7 weeks. It was brewing while in Europe competing, he was performing at a high level. His worst throw was 79m which shows that we were on target. So we knew if he applies himself at qualifying round, he hit big position under massive pressure." When asked as to what was special about Chopra, the Australian coach said, "He leaves his arm back, keeps it way back and throws his body. That is an exceptional skill. He does it naturally. His arm stays back and body attacks." Sports Minister Vijay Goel had already announced a cash award of Rs. 10 lakh for the athlete besides assuring all facilities and support from the government under existing policies.