The England Under-21 international will be out of contract at the end of the season and would be eligible for a free transfer.
Posh chief Barry Fry said in Peterborough Today: "QPR manager Neil Warnock asked if they could take a look at Joe at close quarters and our manager and chairman agreed.
"He was there last week and will be going back there on Monday."
Fry, though, is still waiting for QPR to make an official bid for Lewis, who following a serious knee injury suffered in May made a surprise first appearance of the season in Peterborough's dramatic 4-3 defeat by Barnsley.
"That's as far as it has gone. No offers have been made, but Joe is out of contract at the end of the season when we face losing him for nothing," said Fry.
"He played in a reserve-team game for them and did well."