The National Football League would become the first U.S. professional sports league to blood-test its players for human growth hormone if the players’ union gives its approval to the measure by Thursday’s deadline for the final ratification of the collective bargaining agreement.

The two sides continued Wednesday to negotiate the last remaining provisions of their labor deal, including blood-testing for HGH, in hopes of having the players vote Thursday.

Several people familiar with the deliberations said they expected the union to agree to have players blood-tested for HGH. But the union had not given its formal approval to a drug-testing program for the sport, including blood-testing for HGH, as of late Wednesday afternoon, a spokesman said.

“The players have not agreed to a comprehensive drug-testing program,” said George Atallah, the union’s assistant executive director of external affairs.

HGH is currently on the NFL’s list of banned substances but players are not tested for it. The union previously resisted having players blood-tested for HGH, citing privacy concerns. Gene Upshaw, the former union executive director who died in 2008, had said he wouldn’t allow players to be blood-tested. There would be testing for HGH in the sport only when a reliable urine test for it was developed, Upshaw had said.

But even while some players continued to express reservations about blood-testing, the union took a more receptive stance to the issue during this round of negotiations, announcing that it would listen to what the league was proposing. The NFL cited advancements in the reliability of blood-testing when it made its HGH proposal during these negotiations.

According to several people familiar with the situation, league officials have remained adamant that blood-testing for HGH must be included in this agreement and believe the union recognizes that it must agree or face future scrutiny on Capitol Hill regarding the sport’s drug-testing program.

The blood-testing issue was not all that remained to be settled between the league and the union Wednesday. The appeal process for suspensions of players that are imposed under the sport’s drug and personal conduct policies also was among the final issues being negotiated, people familiar with the deliberations said.

According to those people, who spoke on the condition of anonymity because of the sensitivity of the deliberations, the union was seeking for appeals of suspensions under both the drug and personal conduct policies to be heard by an independent arbitrator. The league, those people said, was willing to allow appeals of suspensions under the drug policy to be heard by an arbitrator, but not appeals of suspensions under the personal conduct policy.

Currently, all such appeals are heard by NFL Commissioner Roger Goodell or a person appointed by him. Players object to having Goodell hear appeals of disciplinary actions that he has taken.

The NFL resumed operations last week after the players put their approval process for their 10-year collective bargaining agreement with the league in motion. Teams opened training camps, and rookies and veteran free agents began agreeing to contracts with clubs. Teams traded players. But the players have not given their final approval to the labor agreement yet, and Thursday is the deadline for that.

Players re-formed their union, which they’d dissolved in March, late last Friday and negotiations on the remaining issues in the labor agreement began Saturday in D.C. The final issues in the labor deal could be negotiated only after the players re-formed their union.

People throughout the sport said Wednesday they remained hopeful the deal would be completed in time for the players to vote Thursday morning. That would allow free agents just signed by teams to participate in practices Thursday afternoon. Those players have been prohibited from practicing until the labor deal is ratified and their contracts become official with the start of the new league year.

The owners previously ratified the labor agreement, and player leaders gave their preliminary approval by recommending that players re-form the union in anticipation of completing and ratifying the deal.

If the players don’t give their final approval to the labor agreement by Thursday’s deadline, the two sides’ settlement of the players’ antitrust lawsuit against the owners would be voided. It’s not clear if the league would take steps to shut down operations again under those circumstances.

Goodell visited the Carolina Panthers’ training camp Wednesday and said in an interview there with the league-owned NFL Network that he and DeMaurice Smith, the executive director of the NFL Players Association, were committed to working out the labor deal’s final issues by Thursday’s deadline.

“We’ll get it done,” Goodell said.

Goodell also told the league’s television channel that, with the new labor deal in place, the league will explore a possibly expanded TV package of Thursday night games for future seasons. The NFL Network current televisions prime-time games on Thursday and Saturday nights in the second half of the season. The league potentially could sell a package of Thursday night games in the first half of the season to a network.