After Griffin lost the starting job on Monday, Jackson compared it to his leaving the Eagles after the 2013 season.
''It's just unfortunate he has to be in this situation like that,'' Jackson said on Tuesday.
''But this is the game we're in, this is the league we're in, this is the NFL. Nothing's for certain. I had to learn that for myself a couple years ago.''
Coach Jay Gruden announced that Kirk Cousins will be the team's starter after Cousins performed well in Saturday's preseason game.
Griffin was unavailable for the game via the league's concussion protocol.
While empathizing with Griffin, Jackson said it ''means a lot'' for the first-team offense just to know who will be under center. He also expects to be ready to play with Cousins on Week 1 after dealing with a sprained right shoulder this preseason.
In the interim, Colt McCoy will play the entire final preseason game Thursday against Jacksonville. Cousins will be the backup in case of injury, Gruden said.
''Unfortunately, we didn't really have time to get a guy in here and teach him the playbook,'' Gruden said.
Cousins completed 20 of 27 passes for 190 yards, a touchdown and an interception against Baltimore on Saturday.
Griffin had completed 6 of 13 passes in two previous preseason games, and the Redskins said he sustained a concussion in the second against Detroit on Aug. 20.
Griffin hasn't said how - or even if - the injury occurred, setting off speculation.
Jackson also endured a frenzy when Philadelphia released him in March 2014 amid suggestions the move was connected to off-field issues. He had career-high 1,332 yards receiving in the 2013 season, and signed with the Redskins in April 2014.
Jackson said Griffin will have an opportunity to bounce back.
''The best advice I could tell him is just to keep his head high,'' Jackson said. ''When he has an opportunity to play again, wherever it's going to be in this league, I definitely think he'll do what he needs to do to get it done.''
Jackson and other offensive players said the offense's principles of balance wouldn't change with Cousins, considered a more traditional pocket passer.
''Our offense is based off the run and opening up everything else off of that,'' wide receiver Pierre Garcon said. ''We're still going to call the same plays we've been calling, and keep moving forward.''
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