Johnson, a Bay Area native, threw for more than 3,200 yards in 2005 and 2006 under Harbaugh's tutelage at the University of San Diego, a Division I-AA school that doesn't offer football scholarships. Johnson's success led to him being a fifth-round draft pick by the Bucs in 2008.
Johnson said that even if he doesn't end up playing for Harbaugh again, their relationship won't change.
"There's a lot of respect there, because I know what he did for me as a player," he said. "I know how much I grew to love him and his family. I felt like it was more than just a coach-player type of thing."