Coach Kyle Shanahan made that announcement Friday after Goodwin missed the entire week of practice with a bruised thigh suffered in last week's loss at Minnesota.
Pettis, a second-round pick out of Washington who caught a 22-yard touchdown pass against the Vikings, will start opposite veteran Pierre Garcon. Another rookie, seventh-round pick Richie James Jr., will be added to the 53-man active roster after being inactive in the opener.
Trent Taylor and Kendrick Bourne are likely to round out the receivers rotation in the 49ers' home opener against the Lions.
Pettis, the son of former Gold Glove outfielder Gary Pettis, is a colorful character who sports dyed blue hair. He also unveiled quite the touchdown dance against Minnesota, making like a cat licking its paws and cleaning its head, after he hauled in his first career scoring pass from Jimmy Garoppolo.
''I think he's very relaxed and very confident being himself all the time,'' Shanahan said. ''That's why he's OK with his cat celebration. Stuff doesn't bother him. He is who he is. He goes out there that first game, I don't think it was too big for him.''
Things remain unsettled for San Francisco at right guard, with Joshua Garnett (dislocated toe) out for Sunday and Mike Person (foot strain) questionable. Should Person be unavailable, Shanahan said undrafted rookie Najee Toran will draw the start. It's quite a rise up the depth chart for Toran, who played at UCLA but was not invited to the NFL combine before eventually signing with the 49ers as a free agent.
Person will be a game-day decision.
Toran said his height (6-foot-2) always was a concern for those evaluating him.
''Everybody had the typical answers: 'You're kind of small,' and things like that,'' Toran said. ''To me it's not a big deal. I just look at it like my heart's the size of you name it. My heart's big. That's what's going to take me a long way, which it has.''
Toran briefly switched from the offensive to defensive line at UCLA before settling in as a starting guard and earning honorable mention All Pac-12 honors as a senior. If he plays Sunday, it won't be his first game at Levi's Stadium. The Bruins played Nebraska in the 2015 Foster Farms Bowl at the 49ers' home venue.
In other injury news for San Francisco, free safety Adrian Colbert and linebacker Malcolm Smith remain questionable with hamstring injuries. Should Colbert be unavailable, Jimmie Ward may slide over from cornerback to take his place. Elijah Lee likely would start in place of Smith, who has been sidelined since the preseason opener.
NOTES: Lions coach Matt Patricia was asked Friday about an NFL Network report that suggested some of his players have been displeased with his handling of the team. ''I don't really acknowledge outside rumors or gossip or anything that doesn't have anything to (do) with our football team,'' Patricia said on a conference call with Bay Area media. ''We're a tight football team. We do a lot of great conversing inside this building and have open conversation about things that are bothering us.''
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