The NFL is examining whether Favre sent Sterger messages and photos while he was with the New York Jets in 2008 and she was a game hostess for the team.
NFL spokesman Greg Aiello said the league had no comment.
Favre could face possible disciplinary action under the league's personal conduct policy.
The allegations arose last month in a report on the website Deadspin.
The site said Sterger wouldn't agree to an interview and acknowledged that it paid a third party for the texts, voicemails and graphic photos, said to be of Favre, that it posted in a video.
The 41-year-old quarterback met with NFL vice president for security Milt Ahlerich last month. Favre has stonewalled questions about the investigation, calling it "a league issue."
Sterger appeared on a Versus TV network show until recently, but it was canceled due to low ratings.
A three-time MVP, Favre has had a rough 20th season in the NFL. He is dealing with two ankle fractures and elbow tendinitis, and took 10 stitches in his chin after getting hit against New England on Oct. 31. The Vikings are 3-5 heading into Sunday's game at Chicago.