Lmao! Pretty self-explanatory but still works with any sports anime character that has a jersey number.
¯\_(ツ)_/¯

『 You may be number __ on the court/field/etc but number 1 in my heart 』❤️

or if you're the athlete then

『I may be number __ on the court/field/rink, but you're always number 1 in my heart』❤️

Kagami: ~You may be number 10 on the court, but number 1 in my heart.
~I may be number 10 on the court but you're always number 1 in my heart.

Kuroko: ~You may be number 11 on the court, but number 1 in my heart.
~I may be number 11 on the court but you're always number 1 in my heart.

Kise: ~You may be number 7 on the court, but number 1 in my heart.
~I may be number 7 on the court but you're always number 1 in my heart.

Midorima: ~You may be number 6 on the court, but number 1 in my heart.
~I may be number 6 on the court but you're always number 1 in my heart, nanodayo~ 💚

Aomine: ~You may be number 5 on the court, but number 1 in my heart.
~I may be number 5 on the court but you're always number 1 in my heart.

Murasakibara: ~You may be number 9 on the court, but number 1 in my heart.
~I may be number 9 on the court but you're always number 1 in my heart.

Akashi: ~You may be number 4 on the court, but number 1 in my heart.
~I may be number 4 on the court but you're always number 1 in my heart.

and for you Haikyuu fanatics:

Hinata: You may be number 10 on the court, but number 1 in my heart.
~I may be number 10 on the court but you're always number 1 in my heart.
+ You may be a 10 on the court, but also a 10 in my eyes. // I may be a 10 on the court but you're a 10 in my eyes.

Kageyama: You may be number 9 on the court, but number 1 in my heart.
~I may be number 9 on the court but you're always number 1 in my heart.

Bokuto: ~You may be number 4 on the court, but number 1 in my heart.
~I may be number 4 on the court but you're always number 1 in my heart.

Nishinoya: You may be number 4 on the court, but number 1 in my heart.
~I may be number 4 on the court but you're always number 1 in my heart.

Sugawara: You may be number 2 on the court, but number 1 in my heart.
~I may be number 2 on the court but you're always number 1 in my heart.

Yamaguchi: You may be number 12 on the court, but number 1 in my heart.
~I may be number 12 on the court but you're always number 1 in my heart.

Nekoma: ~You may be number 5 on the court, but number 1 in my heart.
~I may be number 5 on the court but you're always number 1 in my heart.

And now, your lovely Choba-chan waits for spring because of badminton season ~ :')