Chris Robshaw is not an injury concern for England ahead of their tour to Argentina despite training away from the squad this week.
Robshaw, who was England co-captain against the Barbarians last Sunday, has undergone treatment this week on his ankle and is set to travel with the rest of the squad on Saturday.
England's other concerns, Wasps back-row Nathan Hughes and Sale's Denny Solomona, are expected to be fit for the first Test.
"Everyone is good," Gustard told the Press Association.
"Chris had a sore ankle so missed training on the field but did some different training. The other guys we had concerns about completely trained, so we are happy."
Gustard also pointed towards opportunities for senior players in Mike Brown, Danny Care and George Ford to leave their mark on the more unexperienced members of the squad.
"I think for everyone it is an opportunity to put another claim on an England shirt," he said.
"We always say that you borrow the shirt, it is yours for 80 minutes, it is your responsibility to take the team forward on and off the pitch.
"Those guys (Brown, Care and Ford) have had a great career with England with us over the last year and a half, and we are looking forward to them continuing that in the next two games."