To replace the injured Bob Sanders, the Colts have signed former Kansas City Chief DaJuan Morgan. Morgan played FS for the Chiefs in 28 games over the past 2 seasons. He is a former 3rd round pick as well. Arrowhead Pride gives us good insight into why Morgan was released by the Chiefs last week:
Unfortunately for both sides, that never happened. Morgan never caught on with the Chiefs at safety and once Eric Berry was drafted last April, it assured that Morgan wouldn't have much of a future in Kansas City. So, the Chiefs released him during cut down week and he sat on the open market.
It still is unclear whether Sanders will be placed on IR, as the Colts haven't formally announced anything about it. That announcement should come at some point today. In the meantime, the Colts have waived OT Joe Reitz, signed just last week. My guess is that if Sanders is placed on IR, Reitz will be re-signed. However, your guess is as good as mine whether Sanders will actually be placed on IR.