Kawhi Leonard downplays questions about his leg injury and overall health status after playing 52 minutes in the Raptors' Game 3 win. (0:25)

Last month, the NBA sent a memo to all its team owners detailing a series of new rules about owning sports betting companies and related businesses.

In a nod toward gambling, referee transparency rules have been gradually implemented over the past decade, including announcing officiating crews in advance of games and the publishing of the Last Two Minute Reports.

However, even as the NBA gets deeper into business with sportsbooks, the league has yet to take meaningful action when it comes to injury reporting.

It became an issue again over the weekend when a rib injury to Portland Trail Blazers star Damian Lillard that was kept secret might have contributed to his 5-of-18 shooting performance in a Game 3 home loss on Saturday in the Western Conference finals.

Lillard suffered a separated rib on his left side after being landed on by Golden State Warriors center Kevon Looney in Game 2 on Thursday.

NBA rules require teams to announce whether a player is probable, questionable, doubtful or out by 5 p.m. the day before a game. Lillard's injury was diagnosed Thursday night in Oakland, sources said, but it was not put on the injury report. It was reported by several media outlets after the game Saturday and confirmed by Lillard on Sunday.

"It's there, but it's not something that's affecting anything that I'm doing," Lillard said, downplaying the injury. "Obviously, you feel it, but that's it."

Jeff Chiu/AP Photo

The undisclosed injury to a star player during a playoff series called to mind the hand injury LeBron James suffered when he punched a grease board in frustration after Game 1 of the NBA Finals last year.

After averaging 35 points and shooting 55 percent over his first 19 playoff games last season, including 51 points in Game 1 of the Finals, James' average dipped to 28 points a game on 49 percent shooting after the injury. James had multiple MRIs, but those tests and the injury were not reported by the Cleveland Cavaliers. After Game 1 went to overtime, the Warriors swept the Cavs with a diminished James over the next three games, winning by an average of 17 points.

"Pretty much played the last three games with a broken hand," James said.

It is long tradition in sports to keep certain injuries secret, especially in the playoffs, when opponents can potentially use the information against a team.

"I wasn't much aware of it," Blazers coach Terry Stotts said of Lillard's injury, denying he knew the health status of his most important player. "I didn't know how much it was bothering him until [Saturday]."

Just like with James last year, Lillard played through the injury. The Cavs and Blazers followed the rules. But their stars' performances might well have been affected by the injuries. And that's where the status quo is in question as the league is in the midst of a changing landscape.

Before this season, the NBA signed its first-ever gaming partnership deal, with MGM Resorts. Part of the agreement includes the league providing official real-time data to protect the accuracy and integrity of wagering.

It's a multimillion-dollar deal and part of a wide-ranging effort to encourage gambling on the league. The thought process is that gambling will drive more interest, more eyeballs and eventually more money to the NBA.

So, many of the league's owners who see growth potential are partnering with or investing in gaming companies. In response, the league created a new "20% rule," in which team owners can't have more than a 20 percent ownership stake in a sportsbook or they would be forced to have their team's games excluded from the board.

Yet, there is still no change in injury reporting rules, ground zero for where high-interest games could be influenced. This is especially true in the NBA playoffs, in which a star player's availability or health status could be a huge factor in how the game plays out.

There's significant gray area. Players are protected by federal privacy laws. Also, at this late stage of the season, many players are dealing with various injuries. Several players on each team could be put on the injury report with some malady, which could mask more significant injuries.

Because NBA teams rarely have true practices in the playoffs, using a player's participation on off days loses much of its meaning. This is unlike the NFL, which has a more comprehensive injury-reporting policy and whose practice-participation reports are heavily tracked by gamblers.

One possible option is to require that the results of imaging for NBA players -- be it an MRI, ultrasound or X-ray -- be disclosed by the team. Teams frequently do announce MRIs or X-rays and the results, but many are kept secret, as James' were during the Finals last June.

There would be no gray area in whether a test took place, and it would be a way to reveal any injury concern. For now, that's just a concept and not close to reality.

Jeff Sherman, head NBA oddsmaker at the SuperBook at Westgate in Las Vegas, told ESPN that even if Lillard's injury had been disclosed, he would not have adjusted the line for Game 3. Sherman noted that the situation -- Blazers coming home down 0-2 -- played a bigger role in the Game 3 point spread than an injury that wasn't going to keep Lillard out of the game. Tonight, the Westgate is offering the over/under on Lillard's points in Game 4 at 25, down roughly two points from previous games.

But after Lillard and Portland's performance in Game 3, sportsbooks reversed their position and installed the Warriors as the favorite in Game 4. To say Lillard's health status hasn't played a role in the series would be naive.

When it comes to all these issues, the legitimate side of the sports betting business remains in embryonic stages. The pro leagues are grappling with how to appeal to bettors and get into their pockets at the same time.

But while the NBA has been a leader in this brave new world on a number of fronts, the injury transparency problem remains a real hurdle to overcome.

David Purdum provided additional reporting for this story.