My Player Controllercode isn't working

I’m trying to do the 2D UFO tutorial, and every time I enter in my code it says “The referenced ‘player’ game object is missing” And whenever I try to test it, the player doesn’t move. This is my code.

using System.Collections;
using UnityEngine;

public class CompletePlayerController : MonoBehaviour {

public float speed;
private Rigidbody2D rb2d;

// Use this for initialization
void Start () {

	rb2d = GetComponent<Rigidbody2D> ();

}

// Update is called once per frame
void FixedUpdate () {

	float moveHorizontal = Input.GetAxis ("Horizontal");
	float moveVertical = Input.GetAxis ("Vertical");

	Vector2 movement = new Vector2 (moveHorizontal, moveVertical);

	rb2d.AddForce (movement * speed);
}

Is this script attached to the right Gameobject?

Did you set a “speed” value in the editor? Because you did not set it in the script