Quaternion.LookRotation only on Y axis

Hello,

I make a game and sometime the player (character controller) uses "Quaternion.LookRotation" to lock his view on a gameObject. However, if the gameObject is below or above him, it changes the player controller's rotation and he's not vertical to the ground any more.

My question is: How can I use Quaternion.LookRotation to affect only the Y axis?

Thanks!