Rickard, who swam a heat in the 4x100 medley and took no part in the final, tested positive for a banned diuretic in a rescreening of the sample he gave eight years ago..
The team's six swimmers, including twice 100-metre freestyle world champion Magnussen, could become the first Australians to lose Olympic medals from doping if a Court of Arbitration for Sport (CAS) hearing rules against them.
Magnussen, who was informed of the case in an email from Rickard, said it would be "a long bow" for CAS to cancel the whole team's medals.
"When I first read the message (from Rickard), I was wondering what it had to do with me. But then he said he was a heat swimmer in the medley relay team, so they are thinking about taking your medal," Magnussen told local broadcaster Nine Network late on Saturday.
"I didn’t swim in the heat of that relay ... He didn’t stand there on the podium, he didn’t have an impact on the result of that race.
"You never want to give up an Olympic medal and for some of the guys in that team, it’s the only medal they’ve got. It would be an even bigger blow to them."
Rickard told the team he took over-the-counter medication in the week before the test in 2012, which might have contained the diuretic.
He said he planned to fight any move to disqualify the London results.
Magnussen said it was a "hard situation" for Rickard. "You have to feel for him because how do you defend yourself eight years later? It’s a hard situation for him." (Reporting by Ian Ransom; Editing by William Mallard)