While the Lions take on a Royal XV in Phokeng this Saturday, Johnson's men will be facing the Barbarians at Twickenham ahead of a two-Test series against Argentina next month.
And the three-times Lions tourist has told his players that performing well for England could well see their Lions' dreams realised at some point over the next five weeks.
"Guys like Delon Armitage, Mark Cueto and Steve Borthwick are disappointed as they had every chance of making the original Lions squad," said Johnson, who became the first man to skipper two successive Lions tours when he led Britain and Ireland's elite in 1997 and 2001.
"But the Lions haven't even played a game yet and if someone on that tour does get hurt then the best place for guys like Delon to be is with us playing well."
The Lions have already lost Tomas O'Leary, Tom Shanklin and Jerry Flannery to injury and Alan Quinlan through suspension, while Leigh Halfpenny has not yet joined up with the party following a problem with his quad which requires treatment at home.
Johnson expects more withdrawals during the tour and has told his players of the possible opportunities ahead of them, although he has stressed the importance of concentrating on the job in hand rather than chasing a potential Lions call up.
"All of my players are fully concentrated on England," added Johnson.
"Of course they want to be with the Lions but I know they'll give us everything they can for England.
"We're going into this match (against the Barbarians) with two tough Tests with Argentina ahead of us.
"The players we have to pick from have been reduced because of the Lions and injuries but this is an opportunity for us to see some other players who are back or who have missed out on selection."