<?php
$injuryData = file_get_contents('http://football.myfantasyleague.com/2013/export?TYPE=injuries&L=&W=&JSON=1&callback=');
$array1 = json_decode($injuryData, true);
$playerData = file_get_contents('http://football.myfantasyleague.com/2013/export?TYPE=players&L=&W=&JSON=1');
$array2 = json_decode($playerData, true);

function map($x) {
   global $array1;
   if(isset($x['id'])) {
      $id = $x['id'];
      $valid = array_filter($array1['injuries']['injury'], create_function('$injury', 'return $injury["id"] == "' . $id .'";'));
      if(count($valid) > 0) {
         $x = array_merge($x, array_shift($valid));
      }
   }
   return $x;
}
$output = array_map('map', $array2['players']['player']);
print_r($output);