The 31-year-old was replaced by Lorenzo Cittadini having been forced out with a thigh injury.
But Castrogiovanni has returned to his club side Leicester Tigers ahead of their Premiership trip to Exeter Chiefs on Saturday and been pronounced fit by director of rugby Richard Cockerill.
"They have all reported back fit for duty and that includes Martin Castrogiovanni, which is good for us," said Cockerill of all the Tigers players that featured in the RBS 6 Nations.
The former England hooker admits he will now have to decide whether to bring Castrogiovanni and others returning from international duty straight back into his starting XV.
"It's a strange training week for us," he said.
"Some of the lads are fresh and ready to go and the other third have just played five Test matches on the trot.
"Getting the balance of that right is important and we are experienced enough these days to know how to deal with that."