Both Petravicius, 20, and Zanzala, 18, are regulars for their respective clubs at Under-21 level but are yet to make their first-team debuts.
Petravicius has won five caps for Lithuania, and appeared as a substitute against England last October.
Both players were signed in time for the match against Barnet on Saturday.
Find all the latest football transfers on our dedicated page.
League Two side Stevenage have signed Nottingham Forest winger Deimantas Petravicius and Derby striker Offrande Zanzala on one-month loan deals.