Virender Sehwag can be replaced till the start of this match:
Rajasthan v Bangalore at Jaipur
May 11, 2011 (20:00 local | 14:30 GMT | 16:30 CEST)
Sehwag to undergo shoulder surgery, out of IPL
Nagraj Gollapudi
May 9, 2011
India news: Sehwag to undergo shoulder surgery | Cricket News | Indian Premier League 2011 | ESPN Cricinfo
No he has to be replaced with Reserve Batsman one.