The 49ers have entered the race to land Manning's services next season.
"Filed to ESPN: Third team in Manning race that has emerged is 49ers - Manning worked out for Harbaugh & took physical this week," said Mortensen via Twitter.
Later he tweeted, "Harbaugh and offensive coordinator Greg Roman watched Manning throw at Duke on Tues night; impressive enough to send doctor next day to give physical exam."
The 49ers now appear to be entering the fray for Manning as the third team in the mix with a legitimate chance of landing the former Colts quarterback.
Now it comes down to the 49ers, Broncos and Titans.
The move by the 49ers makes a lot more sense now, considering that the team had not re-signed their own quarterback Alex Smith, the No. 1 overall draft pick in the 2005 NFL draft.
Smith operated under a one-year contract in 2011 as the 49ers advanced to the NFC Championship game, only to lose to eventual Super Bowl Champion New York Giants.
Manning, 36, is coming off a 2011 season in which he was sidelined for the entire year, after enduring four neck surgeries.
Ryan O'Leary is a writer and researcher for Bleacher Report's Video Production Department with seven years experience in the sports industry. Ryan covered the 2010 Vancouver Olympic Hockey Tournament with CTV and has spent time covering the IIHF World Championships, NHL and Collegiate Hockey during his career.