Johnson's struggles a worry for Australia

Australia quick Mitchell Johnson's bid to gain some form ahead of the third Ashes Test suffered a setback against Northamptonshire on Sunday.

Johnson bowled seven wicketless overs for 42 runs, the left-arm quick struggling for accuracy just as he'd done during England's 115-run second Test victory at Lord's, which left Australia 1-0 down in the five-match series ahead of next week's Ashes Test at Edgbaston.

But with experienced fast bowler Brett Lee unfit with a rib injury that has kept him out of the first two Tests, Johnson may well be retained in any event unless Australia bring in Stuart Clark in his place at Edgbaston.

Australia ended the second day of this three-day warm-up match against Northamptonshire on 139 for none in their second innings, a lead of 221.

Opening batsman Phillip Hughes, whose difficulties in the two Tests so far on this tour have been almost as much of a concern as those of Johnson, did at least have the consolation of being 65 not out.

Stand-in opener Andrew McDonald, yet to play in the Ashes, was 69 not out.

However, Hughes - dropped on 28 - was once again troubled by the short ball.

Northamptonshire's first innings of 226 for seven declared saw Australia quick Peter Siddle take three wickets while Alex Wakely (62) and Riki Wessels (50) starred for the home side.

Australia middle-order batsman Marcus North, whose place could be under threat after fit-again pace bowling all-rounder Shane Watson made 84 here on Friday, could only add seven to his overnight 32 before he was caught in the covers off left-arm quick David Lucas.