The source, however, said the injury did not affect Coates' practice participation throughout the year and was more of a nuisance.
On Monday night, Coates tweeted his displeasure at undergoing surgery on his pelvis, then confirmed to inquiring fans that his surgery repaired a groin injury.
Coates played through broken fingers in his left hand in 2016. ESPN reported last month that Coates underwent surgery to repair the hand, but the procedure was for the groin only, a source clarified Tuesday.
Coates played 14 regular-season games and finished with 435 receiving yards, most of which came in the first five games, before the hand injury.
The NFL is investigating the Steelers over injury report protocol involving running back Le'Veon Bell, whose groin injury wasn't listed in the weeks leading up to the AFC title game in New England. Bell left the game because of the groin injury.
The Steelers maintained Bell's injury did not affect his practice participation, and team president Art Rooney II said he's confident the Steelers' response to the league will be satisfactory. Bell missed practice time before the New England game due to a personal matter, not an injury.
Investigations can subject a team to fines, suspensions or lost draft picks.
The league's injury reports are intended "to provide a full and complete rendering of player availability," according to the NFL's 2016 Personnel Report Policy.
"It is NFL policy that information for dissemination to the public on all injured players be reported in a satisfactory manner by clubs to the league office, the opposing team, local and national media, and broadcast partners each game," the policy states. Any disputes in compliance require the team to demonstrate it has acted in a manner consistent with the intent of the policy.