<?php

function get2daysbefore($timestamp) {
    $days = array(
        '0' => '-3',
        '1' => '-4',
        '2' => '-4',
        '3' => '-2',
        '4' => '-2',
        '5' => '-2',
        '6' => '-3');
    $f = date('w',$timestamp);
    return date('dmY',strtotime($days[$f] . ' days',$timestamp));
}

echo get2daysbefore(mktime(0,0,0,10,9,1987));

?>