Quaternion.slerp only on the y axis

Hey I've been making an AI script today, ran into alot of problems if you look at the qeustions I made only today... anyway this is another part of the script:

  using UnityEngine;
     using System.Collections;
 
 public class EnemyScript : MonoBehaviour {
 
     public int health = 100;
     public int rotationSpeed = 1;
     public int moveSpeed = 1;
     
     public GameObject[] gos;
     public GameObject closestPlayer = null;
     public float distance;
     
     void Start(){
         InvokeRepeating("FindClosestPlayer", 0.5f,0.5f);
     }
     
     void FixedUpdate(){
         if(closestPlayer != null){
             transform.rotation = Quaternion.Slerp(transform.rotation, Quaternion.LookRotation(closestPlayer.transform.position - transform.position), rotationSpeed * Time.deltaTime);
             transform.position += transform.forward * moveSpeed * Time.deltaTime;
         }
     }

ok the script does what I want, it looks at the player and wals forward at a certain speed, but it looks at the player in all axis, like if I jump he rotates on the x axis, and I don't want that to happen, I only want the Quaternion.Slerp work on the y axis, this is what I've tried to do:

 using UnityEngine;
 using System.Collections;
 
 public class EnemyScript : MonoBehaviour {
 
     public int health = 100;
     public int rotationSpeed = 1;
     public int moveSpeed = 1;
     
     public GameObject[] gos;
     public GameObject closestPlayer = null;
     public float distance;
     
     void Start(){
         InvokeRepeating("FindClosestPlayer", 0.5f,0.5f);
     }
     
     void FixedUpdate(){
         if(closestPlayer != null){
             transform.rotation = Quaternion.Slerp(transform.rotation, Quaternion.LookRotation(closestPlayer.transform.position - transform.position), rotationSpeed * Time.deltaTime);
             transform.position += transform.forward * moveSpeed * Time.deltaTime;
         }
         transform.rotation = Quaternion.Euler(new Vector3(0f,transform.rotation.y,0f));
     }

I don't know why but this way it doesn't rotate at all, like it goes straight forward, and doesn't rotate to look at the player, help would be apreciated.

Thanks in advance.