Bowman is one of the few remaining links to San Francisco's success earlier this decade that featured three straight trips to the NFC title game and one Super Bowl appearance. Bowman blew out his left knee in the 2013 NFC championship game and missed the entire following season. He worked his way back last season and looked to be back in top form this year before the injury.
Lynch had 12 1/2 sacks and 35 quarterback hits in 30 games the past two seasons for San Francisco. The Niners are tied for 19th in the league with just seven sacks through four games and are looking for players who can bring more pressure.
The Niners hope for better results Thursday when they host Arizona (1-3),Cheap Air Max 720 Free Shipping.
The 49ers could be without another key defensive player as well. First-round defensive lineman DeForest Buckner left Sunday's game with an injured left foot and also had an MRI on Monday. There was no immediate word about the extent of his injury.
San Francisco already lost its other starting inside linebacker, Ray-Ray Armstrong, to a pectoral injury, leaving the defense thin up the middle. Bellore replaced Bowman on Sunday, alongside Michael Wilhoite. Gerald Hodges and Shayne Skov are the backups.
"One thing about him, he's a really intelligent football player," Kelly said. "So, from a mental standpoint I don't think that'll be an issue, but obviously the speed of the game and things like that are obviously something that you can't simulate when you're out. So, he's got to catch back up to that."
Star linebacker and defensive leader NaVorro Bowman was diagnosed with a torn left Achilles tendon on Monday, his second significant injury in less than three years.
His absence was felt immediately Sunday as Ezekiel Elliott had a 23-yard run on the next play right through the hole Bowman would have tried to fill. Elliott added five more carries for 27 yards on that drive and capped it with a go-ahead 1-yard TD run that helped the Cowboys beat the Niners 24-17.
Bowman signed a four-year contract extension this summer worth a reported $44 million that kept him under contract through 2022.
SANTA CLARA,Al Horford Jersey, Calif. (AP) — The losses keep piling up for the San Francisco 49ers.
"We'll have to rally together," Bellore said. "Things will be different defensively. We'll have to overcome him not being in there and we'll have to step up."
"Obviously it's tough news hearing that about Bo," said linebacker Nick Bellore, who is expected to replace Bowman in the starting lineup. "He's a leader in this locker room and more important on the field. He's someone we all look up to."
Bowman suffered the non-contact injury in the third quarter Sunday against Dallas as San Francisco (1-3) lost its third straight game,Vapormax Plus Nere. He had to be helped off the field and was taken by cart to the locker room,Adidas NMD Clearance. An MRI on Monday confirmed the diagnosis,Miami Dolphins Jersey Throwback.
NOTES: The 49ers held a walkthrough Monday but if they had practiced WR Jeremy Kerley (ankle) and CB Jimmie Ward (quadriceps) would have sat out and G Zane Beadles (ankle), CB Chris Davis (quadriceps) and TE Vance McDonald (hip) would have been limited.
The Niners have a roster exemption that allows Lynch to practice without being added to the 53-man roster but coach Chip Kelly said he's hopeful Lynch can play as soon as Thursday.

San Francisco did get one key addition on defense. Outside linebacker Aaron Lynch returned to practice after missing the first four games for violating league rules on substance abuse.