Faf du Plessis has been ruled out of the remaining two ODIs against Pakistan and the first four weeks of the IPL with back trouble. Du Plessis will require six weeks rest and has been replaced by Quinton de Kock in the South Africa squad."Faf has been troubled by low back pain over the past while," Mohammed Moosajee, South Africa's team manager, who is also a medical doctor said. "He was recently diagnosed with bony inflammation in the lumbar spine. His symptoms have worsened over the past two weeks to the extent that it has become necessary to withdraw him immediately in order to allow for rest and rehabilitation as well as a course of hyperbaric oxygen therapy to further facilitate healing."Du Plessis revealed after the second Twenty20 in Centurion just over two weeks ago that he did not bowl himself in the match because of his back condition, although he was tempted to call on his own legspin. "The doctors advised that I don't bowl for a while, until this is sorted out," he said then.Since that has not happened, du Plessis will be sidelined for six weeks. He is certain to miss the first nine matches of the IPL, where he plays for the Chennai Super Kings, and is expected to make a comeback in the week starting April 29. If his recovery goes as planned, he should play seven matches for his franchise as well as any knockout contests in preparation for the Champions Trophy in June.Du Plessis' unavailability leaves a gap in South Africa's middle order which young de Kock may be required to fill. Also in the squad is Dolphins batsman David Miller who could play in du Plessis' place as well.De Kock was dropped from the ODI squad after the series against New Zealand, in which he kept wickets and opened the batting with limited success. He will not be handed the gloves in this series, because AB de Villiers has gone back to wicketkeeping permanently in ODIs, neither will he bat upfront so he will have a change of roles."As disappointing as Faf's injury is, it must be seen as an opportunity for Quinton," Andrew Hudson, convenor of selectors said. "He made a good start to his international career during the previous series against New Zealand and this is a chance for him to build on that."De Kock will play for his domestic team, the Lions, in Tuesday's T20 match against the Titans in Centurion before joining the national squad tomorrow. The fourth ODI takes place in Durban on Thursday and the final match of the series will be played in Benoni on Sunday. Should de Kock feature in both, the Lions will have to do without him on Friday when they play the Warriors but they may have already qualified for the tournament final by then.