The Packers' former quarterback retired March 6 after a 17-year career.
Cornerback Al Harris said on ESPN's NFL Live that Favre also made similar comments to him.
"I know he has the itch to come back and play," Harris said. "If he will or not, I don't know."
The Packers had planned to use Aaron Rodgers as their quarterback for the upcoming season.
"Aaron is our quarterback," Harris said. "Brett's retired. But if he wanted to come back, there would be some guys who wouldn't mind it. I would welcome him back with open arms."
Mortensen also said his source told him the Packers would be reluctant to open the door for Favre because "Brett retired for the right reasons, even though I know his family is tugging on him (to play)."
A message left with the Packers was not immediately returned.
Favre has two years left on his contract at an average of about $12.5 million per season. The Packers placed him on the reserve-retired list in the spring so his salary does not now count toward the cap.
Favre's commitment to retirement has been questioned since his announcement. That talk resumed in mid-June when Favre withdrew from the American Century Celebrity Golf Championship at Lake Tahoe, scheduled for July 11-13.
Tournament spokesman Steve Griffith said then that Favre had to miss the event because of a scheduling conflict.
When he retired, a teary Favre said, "I've given everything I possibly could give to this organization, the game of football, and I don't think I've got anything left to give And that's it. I know I can play. But I don't think I want to."
But less than two months later, he told reporters he might be open to returning if Rodgers was injured.
Favre is the NFL's only three-time MVP and leads the league with 442 touchdown passes, 61,655 yards passing and 160 career victories. He started 253 consecutive regular-season games, more than any other quarterback in history. Including the playoffs, his streak stands at 275.
