The San Francisco 49ers starting lineup will look a little bit different in Week 5 vs. the Seattle Seahawks with a change that may wind up being permanent.
Starting safety Marques Sigle suffered a high ankle sprain in the 49ers' Week 4 victory over the Denver Broncos. That injury is expected to sideline him for several weeks, opening the door for hard-hitting third-year safety Malik Mustapha to push his way back into the starting lineup.
Mustapha will surely be the team's starter as long as Sigle is out, but there's a chance Mustapha winds up holding onto that job even when the second-year safety returns from his injury.
It's important to note Sigle won the starting job alongside Ji'Ayir Brown out of training camp because Mustapha suffered a hamstring
injury early on. Before the injury it was Sigle and Mustapha rotating in with the first-team defense. Once Mustapha went down the battle was over.
With that in mind, we can turn the calendar back almost exactly one year to find another instance of Mustapha working his way into the starting lineup ahead of Sigle.
Last season Mustapha missed the first five weeks recovering from offseason surgery to clean up a previous ACL repair. Sigle, then a fifth-round rookie out of Kansas State, was the starter for those five weeks. He remained the starter when Mustapha returned in Week 6, but Mustapha was heavily involved on defense, playing 21 and 45 snaps in his first two games back before taking over the starting job in Week 8.
There's a chance something similar was happening this year and Sigle's injury only expedited the process. Mustapha played six defensive snaps in the 49ers' season opener, and three in their Week 2 win vs. the Miami Dolphins. In Week 3 against the Arizona Cardinals we saw Mustapha's snap count tick up to 19. Last week when Sigle got hurt Mustapha played a season-high 21 snaps and logged one tackle and one pass breakup.
On the other hand, Sigle was enjoying a strong start to the 2026 campaign and his improvement in coverage stands out. He was also allowing just a 42.9 percent completion rate and a 51.5 passer rating when targeted this year after allowing an 85.2 percent completion rate and a near-perfect 155.7 passer rating a season ago.
What the 49ers should do instead of fully removing Sigle from the lineup like they did last year is keep some sort of three-safety rotation where they can utilize both Mustapha and Sigle's different skill sets. Mustapha fits best as a box safety whose physicality shines in the run game, while Sigle fits best as a deep safety whose athleticism and improvement in coverage have helped the 49ers shut off the faucet on explosive plays.
Ideally a team would have two awesome safeties they feel great about starting every game. San Francisco's group doesn't have that level of player, but they have enough talent between the skill sets of Mustapha and Sigle to get high-level production at the spot alongside Brown. It's going to take some creativity, but once Sigle's healthy he should continue being heavily involved in the 49ers' defense even if he does lose his starting job.
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This article originally appeared on Niners Wire: 49ers have new starting safety in Week 5, will switch be permanent?
