Vikings quarterback Tarvaris Jackson missed his second straight day of practice Thursday, and it's appearing more likely that veteran Kelly Holcomb will start for Minnesota against the Chiefs. Jackson injured his groin in the fourth quarter against Detroit last Sunday, and has been unable to participate in the first two practices of the week. But Vikings coach Brad Childress was still playing it coy Thursday, saying the window is still open for Jackson to recover and play at Arrowhead Stadium on Sunday.