Another football question

I saw that a referee got injured today. It was minor and he completed the game but it made me wonder about the procedure for this. Obviously an official could be injured on the field and unable to continue the game. Is there a standby referee waiting to step in? Or do they close one of the officiating positions and fill in?

IIRC they rotate everyone else around, and play without one of the deep guys (probably the side judge). Oddly there’s an alternate in the NBA (or at least there used to be-perhaps before the 3 ref system).

They also make do with the three remaining umpires in Major League Baseball when an umpire gets injured. Home plate obviously stays occupied by an umpire no matter what, and the other two umpires move around depending on whether runners are on base (all the better to see force plays).