Rioli is facing a ban of up to four years for allegedly tampering with his urine sample last August during a routine drug test.

The 24-year-old fled home to the Northern Territory when the adverse findings were made public last September but he flew back to Perth in January to rejoin the club for pre-season training.

Simpson confirmed on Tuesday that Rioli had left Perth again, and he's not sure when the premiership forward will be back.

"He drove back last week," Simpson said.

"He's expecting the birth of his second child, the baby is due on March 13.

"Whether he comes back and lives here (after the birth), or stays in Darwin, or goes back up to Tiwi, we're still working through that."

Simpson said the club was still in the dark about when Rioli's case will be heard.

"We're waiting like everyone else," he said.

"The way these things work I don't think they get that transparency."

Although Rioli's return to pre-season training was brief, he was able to reconnect with the players.

"It was a chance for him to bond with the players for a couple of weeks, train, just be normal," Simpson said.

"He loves football, he loves being on the track."

Meanwhile, Simpson isn't sure whether star defender Jeremy McGovern will be fit for the round-one clash with Melbourne on March 22.

McGovern underwent surgery during the summer to fix an achilles-related heel complaint.

Although McGovern is now pain free and set to rejoin main training next week, Simpson isn't sure whether the four-time All-Australian will be fit for round one.

"If everything goes right he might be available," Simpson said.

"It has just taken a little bit longer to settle down - the achilles - but now he has turned a corner

"We are not putting any pressure on him. It is not all about round one as we all know.

"It is the second pre-season where he has missed a fair chunk of training. It is a pretty long season as we know and we will see how we go."

Australian Associated Press