Morgan’s eighth international try was the highlight of a typically impressive all-round individual display in defence and attack.
“Jac was outstanding and the try he scored was unbelievable from that distance,” he said.
“It’s a blow. Not only just the player, but the man. With this group, we spoke about having tough moments in this journey.”
Tandy named Leicester’s Tommy Reffell and uncapped Ospreys flanker Harri Deaves as potential options while Cardiff’s Taine Basham could also be considered.
“We’ll definitely call someone up and will discuss that after assessing things in the next 24 hours,” said Tandy.
“We’ve got some really good players. Tommy [Reffell] is an outstanding international, playing well for Leicester while Harri Deaves has been unbelievable for the Ospreys for a consistent period. So we’ve got options.”
Dragons number eight Aaron Wainwright was also forced off the field in the second half with “cramp”.
Tandy added: “We’ve got to look at him and assess him over the next couple of hours.”
