Milligan has damaged a disc in his spine which flared up in the yoga session then got worse in last weekend's game.

Now he is taking cortisone tablets to help the healing but which are normally banned.

Milligan has been given permission by ASADA to undergo the treatment, but is prohibited from having the drug in his system on match days.

He has been withdrawn from this weekend's crucial game against Central Coast Mariners as a precaution to avoid any danger of a lengthy ban if the cortisone was to show up in a post match drug test.

"It's fine, I've got approval to take it during the week but it's not worth taking the chance on the weekend," Milligan told Sydney's Daily Telegraph.

"You would be looking at a substantial ban. But it's not a matter of life or death, so we decided it was best to get it right for the next game.

"It's like a cortisone but I need to take it because my back has been playing up again. So I've been cleared to use it (by ASADA) but I can't take it on match days.

"Most players get an injection but my problem is more disc-related so it needs to settle a broader area.

"I aggravated it last Wednesday doing yoga. It didn't settle by the weekend and it flared up again on Sunday and Monday.

"This is more extreme action but I don't want to be messing around with my back at 22."

He added: "I spoke to Kossie and we decided to sort it out now so I'm right for next week and near 100 per cent rather than playing and having an interrupted week before Adelaide.

"So I'll start taking the tablet and relax before some light jogging."