The Frenchman has not played a competitive match since January 2012 and has been without a club since leaving German side Werder Bremen in the summer.
Silvestre, 35, spent time training with Sir Alex Ferguson's side in October to regain his fitness in order to find a new club.
Timbers club owner Merritt Paulson and head coach Caleb Porter believe the versatile player will add some much-needed experience to the side's defence ahead of the new campaign.
Portland Timbers finished eighth in the Western Conference last season.







