At 14 minutes and 24 seconds into the fourth quarter, the injury took place.
When Kupp came down from attempting to grab the ball, a Cardinals defender rolled up on his ankle.
Head coach Sean McVay told reporters, "I just know it didn't look good."
As one listener put it, "It didn't sound nice."
McVay noted that he had not spoken with the club's medical team, so he did not have an official update on Kupp's condition.
According to NFL Media, Kupp may be out for a while, but the injury is not life-threatening.