His arrival will help cover the gaps left by injuries to Joe Ledley and Peter Whittingham, the former out for a few weeks, the latter possibly 3 months.
Routledge is an exciting wide player who in the past has scored a couple of times against City. In the 2003 / 2004 season, City's fist back at this level, he scored at both Selhurst Park and Ninian Park as Palace did a league double over the Bluebirds.
If this comes off it's an excellent signing and follows the capture last week of Michael Chopra.