http://www.dispatch.com/live/content/sports/stories/2010/10/15/holmes-eases-tressels-worries.html?sid=101
Ken Gordon wrote about it before the Wisconsin game. Here's the excerpt about Keels in the article:
Surgery silences Keels
Paul Keels, play-by-play announcer on the Ohio State football radio network, will miss Saturday's game at Wisconsin after undergoing emergency abdominal surgery Tuesday.
Keels is expected to make a full recovery but likely will remain hospitalized until early next week.
In his place, Marty Bannister will take over the play-by-play duties alongside analyst Jim Lachey. Dan Fronczak of Channel 10 will replace Bannister as the sideline reporter.
Apparently it was for "intestinal blockage" and the surgery was successful. Hope he gets better because listening to the buckeyes on the radio isn't the same without him.