Just be yourself and feel confident when speaking entirely in Chinese.

English is not necessarily useful as not everyone in Europe speaks English.

Anyway, any group of people who come to China to learn football must be profoundly wise, understanding and tolerant.  

Less tolerant individuals would have chosen to go to England (if they wish to speak English) or Germany (if they are interested in winners and not losers).

Don't worry!  Teach with confidence entirely in Chinese, so that your teaching is not affected in any way.

Beckham when he came to China to teach youngsters football did not try to speak Chinese.

Use a lot of body language and personal demonstration.  Concentrate on movements and techniques.  You are teaching football, not Confucian philosophy.  You don't need words.

我是认真的，你真的不用担心，满怀信心的用中文授课就可以了。

Start by forgetting the word " soccer ". This word is tabu in Europe. Only the north americans use it. If you say in France " I play soccer " everybody is going is to look at you surprised. No, we say " football" . You know the game played with a ball, that you strike with the feet.

I am curious what kind of object you are confronting? children, teenagers, or adults? Perhaps you may demonstrate your skills with your gesture or posture or even sign langugage as much as you can in face of some embarrassing circumstance. It is supposed to be the point that your skills in soccer counts.

If it really bother you... if I were you I`d invete an interpreter. Why not? If it s really important to you.

And maybe I would start some course specialized in this very sphere of activity.. I mean sport and football in particular.

But, sure, I agree with the previous comments - the most important is to be confident. They should try making efforts to understand you too.

Good luck!