Charles Robinson of Yahoo Sports reported the league had a firm co-founded by then-NFL communications chief Joe Lockhart, The Glover Park Group, conduct the poll.
The survey had questions on a number of NFL-related issues alongside Kaepernick, who was the only specific player mentioned. Roger Goodell was reportedly among the NFL executives who received the answers to the poll questions.
The former San Francisco 49ers quarterback filed a grievance against the league in October. He argued NFL owners colluded to keep him unsigned after he protested racial injustice and police brutality by kneeling during the national anthem.
According to Robinson, the poll asked fans if they thought Kaepernick should be signed and whether they thought his decision to not stand during the anthem was the reason he wasn't with a team.
"The poll could create a significant point of contention in Kaepernick's collusion complaint against the NFL, raising the question of why the league conducted opinion research with its fan base about the former San Francisco 49ers quarterback," Robinson wrote. "The existence of polling data on Kaepernick could also raise the question of whether the research went beyond high-ranking NFL executives to ownership groups or other team personnel who could have signed the quarterback."
On Monday, Mike Florio of Pro Football Talk reported the collusion investigation revealed internal franchise documents suggesting some teams viewed Kaepernick as talented enough to remain a starter in the league.
The topic of protests during the anthem has been in the headlines again this week, after the league instituted a new policy prior to the 2018 campaign Wednesday.
Ian Rapoport of NFL Network shared the new rules, which require players to stand for the anthem if they are on the field, with teams subject to fines if their players don't stand. Players have the option to remain in the locker room until the song ends if they don't want to stand.