Pro tennis players

I was really surprised that Nick withdrew from singles with left knee in Atlanta
but played doubles and reached final and won. is that allowed situation?
 
I was really surprised that Nick withdrew from singles with left knee in Atlanta
but played doubles and reached final and won. is that allowed situation?

He did it. So, it was allowed. Nick stay doing antagonistic, petty and privileged shit. But because he’s “cool”, brings in non tennis fan viewers and is non-white people keep making excuses (I am black btw). His actions pretty much said: this tournament is too small for me to wear myself out, I still want a check and some time on court.
 
He did it. So, it was allowed. Nick stay doing antagonistic, petty and privileged shit. But because he’s “cool”, brings in non tennis fan viewers and is non-white people keep making excuses (I am black btw). His actions pretty much said: this tournament is too small for me to wear myself out, I still want a check and some time on court.
Before 1R singles match his knee was so bad and right after it was fully recovered like a miracle.