The news comes only a fortnight after the Blues discovered luckless ruckman Matthew Kreuzer had a hairline fracture in the same foot that forced him out of most of last season and which will now see him in a moonboot for another month before being reassessed.

Walker pinched the cartilage in the knee that was operated on in July last year and has needed to have a second procedure to repair the damage to the meniscus. The club said he is expected to be sidelined for six weeks, which would put him in danger of missing the Blues' first game against Richmond  on April 2.

"It's unfortunate that Andrew's had another setback with his knee, however we are looking forward to him returning to full training soon and he remains in contention for round one," Carlton's head of football Andrew McKay said.

Blues captain Murphy felt tightness in the calf during Friday's intra-club match. Further scans confirmed a strain and he will be sidelined for two to three weeks but McKay said he would be fit for round one.

Small forward David Ellard also has a calf strain which will keep him out for three weeks while forward Troy Menzel has almost recovered from a quad injury.