​SANTA CLARA — What was that Mike Tomlin said a week or so ago? The Browns are gonna Browns? Well, along the same lines, the Niners are gonna Niners.There’s no other way to explain the endless cycle of injuries.Another season that started with legitimate Super Bowl aspirations, backed up by their play in the first couple weeks, officially went off the rails Friday with the news of their latest blow.A defensive line that was already on life support lost its beating heart when Nick Bosa pulled his calf in practice on Thursday. The 49ers will be without their ferocious edge rusher Sunday against the Cardinals and for some time beyond that, coach Kyle Shanahan said after practice Friday.Bosa was going through individual warmups before the Niners held a walkthrough Thursday when he suffered the injury doing high-knees, according to Shanahan. He is expected to miss “around a few weeks,” Shanahan said, but the 49ers opted to keep him on their active roster.Nick Bosa (97) of the San Francisco 49ers looks on before a game against the Miami Dolphins at Levi’s Stadium in Santa Clara, California, Sunday, Sept. 20, 2026. Getty ImagesSan Francisco’s injured reserve is already so crowded that it risks running out of spots for players designated to return. Teams are allotted eight spots, and there are already seven 49ers on IR that they hope to get back, plus Bosa and two others dealing with high-ankle sprains.It’s an absurd amount of attrition this early in the season, even for a team as terminally injured as the 49ers. The losses hurt and the roster crunch is real, but the Niners have so far been able to count on their next-man-up philosophy to cruise to a pair of 20-point wins to start the season.So much for that without their five-time Pro Bowl defensive end and 2022 Defensive Player of the Year. There is no player — not even quarterback Brock Purdy — as irreplaceable as Bosa.Nick Bosa (97) of the San Francisco 49ers pressures Malik Willis (2) of the Miami Dolphins during the third quarter of a game at Levi’s Stadium in Santa Clara, California, Sunday, Sept. 20, 2026. Getty ImagesEspecially not when five of the other 10 defensive linemen on the 49ers’ initial 53-man roster have also gone down, and with the edge rusher supposed to line up opposite Bosa, Mykel Williams, ineligible to come off the Physically Unable to Perform list until at least Week 5.“Losing Bosa was rough,” Shanahan said in the understatement of the season. “Losing six out of the 10 D-linemen in the last two weeks was a little unusual. … I do understand the challenge of not just losing Bosa but the number of guys there in two weeks. That will be a challenge on everyone else. We’ve got some new guys in here that will have to step up.”The 49ers’ defensive line has been decimated by injuries to C.J. West (bone chips/knee), Sam Okuayinonu (broken foot), Alfred Collins (torn patellar tendon) and James Thompson Jr. (ankle sprain). Their pass rush took another blo