Just saw this on Cricinfo:
Don't think it's anything too serious or else he wouldn't be in the starting XI. Hopefully it doesn't affect him too much during the match.
Cricinfo said:McCullum was clutching his back after landing while attempting to take a catch during training. Guptill and McIntosh to open the batting.
Don't think it's anything too serious or else he wouldn't be in the starting XI. Hopefully it doesn't affect him too much during the match.