In the ultra-scrutinised world of U.S. professional sports, there is still one line that no one has ever crossed.
There is still not a single openly gay player in any of America's major professional sports leagues.
In a country with openly gay politicians, entertainers and even soldiers, professional sports has become a final frontier.
Questions are now being asked why sports, which helped play a key role in changing public opinion on racial discrimination, is out of step with the rest of American society.
Nowhere has the issue become hotter than in the National Football League (NFL), the most macho of America's pro sports.
In the days leading up to this year's Super Bowl in New Orleans, San Francisco 49ers cornerback Chris Culliver told reporters he would not welcome a homosexual teammate into the locker room.
He later retracted his comments but reports have since emerged of NFL teams asking college players about their sexuality ahead of next month's draft.
This prompted the New York State attorney general to send a letter to the NFL, urging the league to take action and adopt a formal policy of sexual discrimination.
Culliver's comments are not typical of the attitude of all professional sportsmen. Indeed, there are several high-profile NFL players, most notably Chris Kluwe and Brendon Ayanbadejo, who have advocated for gay rights.
Both believe it is only a matter of time before a professional player comes out publicly.
On Monday, CBS reported there was at least one current NFL player considering coming out.
"Based on interviews over the past several weeks with current and former players, I'm told that a current gay NFL player is strongly considering coming out publicly within the next few months," CBS reported.
The report said the player's identity was unknown but he was more concerned about the public response than the reactions of team mates.
CBS quoted free agent linebacker Scott Fujita as saying he did not believe sexuality would be an issue in the locker room.
"I honestly think the players of the NFL have been ready for an openly gay player for quite some time now," Fujita said.
"Trust me, the coming out of a player would create much bigger waves outside the locker room than inside. The way I've seen the conversation around LGBT issues evolve, especially in the past few years, has been encouraging.
"Guys are more accepting than they used to be."