The Netherlands Under-21 star has picked up a thigh knock in a game for the Primavera side on Wednesday, and could be out of action for a number of weeks
The 19-year-old featured in the Primavera game against Padova on Wednesday in order to gain match rhythm, but was forced to leave the pitch in the closing stages of the first half due to a hamstring problem after previously finding the net in the 12th minute.
It's not yet exactly known how long Castaignos will be unavailable due to the knock as he has yet to undergo further examination, but the promising forward is unlikely to take part in Saturday's game against Cagliari.
Castaignos joined Inter from Feyenoord in the summer of 2011, but has so far been struggling to secure regular first-team action at the Nerazzurri.
The Netherlands Under-21 starlet has made six Serie A appearances this term, scoring once in the process.