Aussie batting line up since start of 02/03 Ashes series (partially to shut up the Lehmann naysayers
):
Langer - 22 tests, 48.26 average, 7 100's & 4 50's
Hayden - 22 tests, 70.25 average, 11 100's & 5 50's
Ponting - 20 tests, 72.22 average, 8 100's & 6 50's
Martyn - 16 tests, 45.96 average, 2 100's & 7 50's
Lehmann - 15 tests, 60.04 average, 5 100's & 6 50's
Katich - 8 tests, 44.25 average, 1 100 & 4 50's
Gilchrist - 22 tests, 44.55 average, 4 100's & 5 50's
Looks to me that Martyn is the most vulnerable as he is averaging nowhere near as high as Lehmann (whose more than useful bowling could be important in India aswell), doesn't fulfill any specialised role (Langer - opener, Gilchrist - keeper & vice-captain) and is up against two players with youth on their side in Katich and Clarke.
However, I think it is most likley that Clarke will be sat back down and be told to wait for his chance to come around again. Quite rightly IMHO. Australia has a setlled team at the moment with no dire need to replace anyone. They can afford to wait for someone to have a
real dip in form, not a 'he hasn't been averaging over 55' dip, or the retirement announcements that may be sooner than you think with youngsters waiting in the wings (remember Hussain?).