In a truly heartbreaking moment of miserable luck, linebacker Dre Green injured himself as he jogged onto the field after a punt.
An errant step had his knee buckling, sending him to the turf in pain.
Greenlaw went straight into the medical tent. A few minutes after the injury the CBS broadcast revealed that the team fears he suffered an Achilles injury. He had to be carted off the sideline. He is not expected to return.
Considering the high-profile Achilles tendon injuries that have happened this year on artificial turf, notably Aaron Rodgers, it's worth noting that Allegiant Stadium has a natural grass field.
Greenlaw was replaced by Oren Burks, who spent the week limited in practice with a shoulder injury. He was a full participant on Friday and didn't carry an injury designation going into Super Bowl Sunday.
The 49ers drafted Greenlaw in the fifth round of the 2019 NFL Draft out of Arkansas. He became a rookie starter at linebacker, starting 65 total games in his first five seasons.
Losing Greenlaw is a blow, especially because the San Francisco defense is already playing without the likes of defensive end Clelin Ferrell, safety Talanoa Hufana and outside linebacker Drake Jackson. They were all lost to season-ending injuries.
At the time of his unfortunate slip, Greenlaw already had three tackles to his name.
Of course, football is a game that requires a "next man up" mentality. The 49ers have managed to survive with other injuries. They've got another one to overcome.