Which Kos clearly is now. Being a dog to his employer
The option stated in the contract, is that it is optional for Arsenal to extend it and NOT Koscielny, he has no right or claim to whatever decision Arsenal makes,and if Arsenal chooses to extend it, like Arsenal has, then he is contracted to Arsenal for an additional year whether he wants it or not. Simple as that.
And still being contracted to Arsenal, he is liable to whatever terms that is spelled out in that contract he agreed and signed since day 1 till the very last day of his employment which has now been extended an additional year. Any other way and it will be a BREACH in contract.
As things remain the only way out for Koscielny is to buy out the remaining year, or convince Arsenal to mutually terminate. But as far as his contract goes, he is legally contracted to provide an additional year's service to Arsenal because Arsenal exercised that option.
Also please use some common sense, even the stupid example you gave, "both employee and employer can have option to extend or to quit." If the employee has any say or power to decide things even if the employer from your stupid example wants you to stay after probation but you want to leave you can just leave without any repercussion and the employer wouldn't have been able to do a thing. It is obvious it doesn't work that way with football contracts because if it was like as you said, Koscielny could've just left and there would be no consequences. He would not have needed to beg Arsenal for mutual termination and there would have been no need to pull off any of his stupid antics like refusing to go on tour like a spoiled child.
Also if Koscielny had any right to quit the contract at all, he could've just walked away and it wouldn't be regarded as BREACH of contract.
Please get your facts right before spouting bullshit from your hole up top instead of from the hole down below.
don't be hypocrite.
your aubaclatyang also had refused to train with dortmund. if you are not hypocrite you should condemn him as unprofessional too.