The NFL and the NFLPA have intensified negotiations to implement HGH testing for the first time in league history in addition to revamping its drug testing policy after three years of battles, per multiple sources familiar with talks on a revised policy.

While the sides are trying to come to an agreement before Sunday's slate of regular-season opening games, sources say there remains a "fragile" state of talks as the proposed revised policy is being finalized. Sources on both sides caution on the basis of sensitive negotiations that have previously imploded.

"Players who have been to any collective bargaining negotiation understand that we never describe them as 'very close,'" NFLPA president Eric Winston said in a statement. "We look at every issue we can to improve the rights and benefits of players. This process takes time, it takes creativity and it is never easy.

"We want to get a new agreement in place but we understand the responsibility we have to the players and to the game. It is critical that we get this right."