Pritchard, 20, a reported target for Liverpool recently, has impressed for Spurs' youth and reserve sides but has yet to make a first-team appearance for the Barclays Premier League club.
Posh chairman Darragh MacAnthony said via Twitter: "Delighted to announce loan signing of Alex Pritchard from Spurs who has joined until end of season. He is a fantastic young talent.
"Myself & Gaffer watched this young lad destroy our reserve team couple weeks ago scoring 4 goals from playing left wing / right wing / attacking midfield."
