Paolo Odogwu has been called up to the England U20s squad for the World Rugby U20 Championship in Georgia as an injury replacement.
Backs Ali Crossdale and Dominic Morris have been ruled out of the remainder of the 2017 World Rugby U20 Championship through injury.
The Saracens pair sustained hamstring injuries in England's win over Samoa on Wednesday and they will be replaced in the 28-man squad by Sale Sharks' Paolo Odogwu and Bath's Darren Atkins.
Vass paid tribute to Crossdale and Morris - who both scored two tries against Samoa.
"It's really disappointing for them, in the first game as well; and they didn't really get to experience tournament life," he said.
"They both played really well in the game so it is a big loss to lose two very good, exciting players with talent and speed."
Odogwu and Atkins will arrive in Georgia ahead of England's Pool A game against Australia on Thursday 8 June.
"It's exciting for them," added Vass. "They've got a massive opportunity because they are going to have to play at some point. It's also exciting for us as they are both very good players and will add a different aspect to our game."
England World Rugby U20 Championship fixtures:
England 74 v 17 Samoa: Wednesday 31 May - Avchala Stadium
England v Wales: Sunday 4 June - Avchala Stadium (5:30pm KO BST)
England v Australia: Thursday 8 June - Avchala Stadium (5:30pm KO BST)
Semi-finals and knock-out matches (Tuesday 13 June) Details TBC
Final and knock-out matches (Sunday 18 June) Details TBC