It's not so much a question of whether Hojbjerg should come on now, but whether he should be on for Davis (who hasn't been good) or one of the other two on yellows.
He was drifting upfield, maybe a bit too much, but maybe not. Sane was onside because of CB. Not really Martina's fault. Combination of giving the ball away in bad area and a fantastic head's up pass from Fernandinho.