不是应该说become champion吗?
由于冠军是“独一无二”的,所以其前的冠词通常可以省略。又如:
She became champion in 1964. 1964年她成为了冠军。
I fulfilled a childhood dream when I became champion. 我成为冠军,圆了我儿时的梦。
但这类不定冠词的省略不是必须的,有时也不省略。如:
She has the potential to become a champion. 她有潜力成为冠军。(朗文)