But Leonard, a veteran of three Lions tours, insists history demonstrates Robshaw can still have a role to play Down Under.
"You have to be quite mindful of the fact that on previous Lions tours the squads that have left these shores to go to New Zealand, Australia, South Africa, change," said the former prop.
"With the injuries that happen on these tours I wouldn't be surprised if Chris Robshaw was called up.
"He's player that's played and led England so well this year, I still think he will feature at some stage."
Robshaw's coach at Harlequins, Conor O'Shea admits the flanker was bitterly disappointed by his omission
But he insists he would be ready to jump on a plane to answer any injury SOS.
"He's been pretty down," said O'Shea
"Judged on fitness and form, he should be on the plane. I'm really, really disappointed for him.
"Gats has put his faith in other people but I would never criticise Warren - he is the most successful coach in the northern hemisphere. I'm sure Chris will get on the plane (eventually).
"He was more disappointed than when he was left out of the World Cup squad. With all the scrutiny he has been under for so long - leading England to four wins and two man-of-the-match awards in the Six Nations, leading them to victory over the All Blacks - he was under the microscope and others could fly under the radar and have off days.
"You value Chris more when you've had time with him - England found that out. If he gets the opportunity, you will see his value very, very quickly.
"Chris is ready to go. I don't think he needs to go to Argentina (with England), he can just go out to Australia and play."