Arians missed practice Thursday with the flu, but he later returned to the Colts and was at practice as the team prepared to face the Ravens. The Colts told Jones that Arians is "fine," which is great to hear, and NFL.com's Ian Rapoport reported that Arians was joking in the hospital and wanted to coach, but doctors won't let him leave with what they believe is an inner ear infection or a virus.
Clyde Christensen will call the plays for the Colts on Sunday.
It's yet another obstacle for this Colts team that has overcome so much this season. Arians did a brilliant job as interim head coach while Chuck Pagano went through leukemia treatments. Pagano returned to the team before a victorious Week 17 game against the Houston Texans.
If nothing else, this Colts team knows how to adjust on the fly.
UPDATE: NFL.com's Ian Rapoport is reporting that Arians' illness is believed to be a reaction to medication he took this week. The plan is to keep him in the hospital overnight. He will travel back to Indianapolis on Monday.Follow Gregg Rosenthal on Twitter @greggrosenthal.