After initial fears that 49ers linebacker Kwon Alexander might have suffered a serious injury Thursday night in Arizona, the team now is more optimistic about his status.

NBC Sports Bay Area's Matt Maiocco reported that Alexander wasn't immediately diagnosed with a torn pec and "appears to have good range of motion."

The #49ers have some level of optimism concerning LB Kwon Alexander's chest injury. It was not diagnosed immediately as a torn pec, which would be a season-ending injury. He will undergo MRI on Friday to determine the extent of the damage. He appears to have good range of motion. — Matt Maiocco (@MaioccoNBCS) November 1, 2019

Earlier, 49ers coach Kyle Shanahan had told reporters after the 28-25 win over the Cardinals that Alexander will undergo an MRI on his chest Friday.

"We're guessing somewhere with his pec," Shanahan said.

If Alexander indeed suffered an injury to his pectoral muscle, it very likely could end his season. That would be a huge blow to the 49ers' defense, considering Alexander entered Thursday's game ranked second on the team with 34 tackles.

For reference, Houston's J.J. Watt tore his pectoral muscle last weekend against the Raiders, and has been ruled out for the remainder of the season.

Alexander's injury occurred midway through the fourth quarter against the Cardinals.

It looks as if Kwon Alexander has his shoulder pads off and is sitting on the bench. — Matt Maiocco (@MaioccoNBCS) November 1, 2019

#49ers injury update

LB Kwon Alexander (chest) is OUT.

— Matt Maiocco (@MaioccoNBCS) November 1, 2019

LB Kwon Alexander's chest injury - and the fact he was ruled out immediately - is very alarming. — Matt Maiocco (@MaioccoNBCS) November 1, 2019

Alexander did not register a tackle on defense before he was removed from the game.

49ers' Kwon Alexander to undergo MRI for possible pectoral injury originally appeared on NBC Sports Bay Area