Remove multiple spaces and filter in the_content and the_excerpt || get_the_excerpt.

functions.php

<?php
/*
* Filter in functions 'the_content' and 'the_excerpt'
*/
add_filter( 'get_the_excerpt', 'esc_spaces' );
// add_filter( 'the_excerpt', 'esc_spaces' ); // Don't required
add_filter( 'the_content', 'esc_spaces' );
function esc_spaces( $content ){
    if ( '' == $content )
        return $content;

    $safe_content = wp_check_invalid_utf8( $content );
    $safe_content = preg_replace( array(
        '/\s{2,}/',
        '/[\t\n]/'
    ), ' ', $safe_content );

    if ( '' === $safe_content ) {
        return $safe_content;
    }

    /**
    * Filter the content remove multiple spaces.
    *
    * @param string $content      The content prior to being escaped.
    * @param string $safe_content The text after it has been escaped.
    */

    return apply_filters( 'spaces_escape', $safe_content, $content );
}