Unity can't assign a game object.

Error: The variable player of playerFire has not been assigned.
I had draged and droped FighterMedium(FBX) to the player property. But it saws me the error of upside you can see. Watch the picture for more information.


And here’s my code-
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class playerFire : MonoBehaviour
{
public GameObject selfobj;
public GameObject player;
void Start()
{
transform.eulerAngles = new Vector3(0, -90, 0);
transform.position = new Vector3(player.transform.position.x, -1.1f, player.transform.position.z);
}
void Update()
{
transform.Translate(1, 0, 0);
Destroy(selfobj, 5);
}
}
Can you help me why this error is causing? You can ask me for more information.

Guys, don’t need answers now, I’ve found my problem by myself! The problem was actually, the bullet prehabs which were I instantiating where player cannot be seted. So I used GameObject.Find() to get the position of the player.