Ross Moriarty is "absolutely gutted" at missing out on next month's autumn Test series, according to Dragons forwards coach Mefin Davies.
Pivac has told the British and Irish Lion to improve his all-round game to claim a place for the Six Nations.
Davies says Dragons feel Moriarty's "hurt" and backed him to prove a point in Sunday's derby against Ospreys.
"This is actually the best I've seen Ross, both personally and as a player," said former Wales hooker and Grand Slam winner Davies.
"He has been available and has played virtually every minute of every game so far, so I feel his pain. He's gutted, absolutely gutted, but I know Ross will turn up on Sunday.
"Through the changes that have gone on [at Dragons], he has been a real positive. He's trained hard, spoken up as a senior player and shown leadership. There's no nonsense with Ross and you need that at times.
"But most importantly he has actually been performing well over a run of games and that's the bit that hurts the most for all of us here at the Dragons and especially Ross."
Pivac admitted it was a tough call to leave out Moriarty, who missed the summer tour to South Africa following knee surgery.
The Wales coach also insisted the autumn matches against New Zealand, Argentina, Georgia and Australia present a chance to run the rule over other players.
He added: "We know Ross is good. His target is the Six Nations. We've asked him to work on a couple of things in his game which he'll go away and work hard on."
Moriarty is not the only Dragon with a point to prove this weekend after both hookers, Elliot Dee and Bradley Roberts, missed out to Ospreys' Dewi Lake.
"I feel for them. We would have hoped one, if not both, would have got in the squad because they are fighting for a position and playing well," said Davies.
"The important thing is that they are game-ready for any opportunity that may still come.
"That's also the great thing about these derbies so soon after Wales selection. There are those players who are on a high and those who are out to prove a point."
Meanwhile, Taine Basham has received some positive news after doctors ruled his dislocated elbow against Cardiff on Saturday does not require surgery.