The Latics boss, whose grandmother is Gibraltan, turned down the offer despite being encouraged to take it by club chairman Simon Corney.
BBC Sport quotes Johnson as saying: "I just got a phone call from an agent saying 'they are searching for players that could be eligible, would you be interested?'
"I was shocked. I rang the chairman and the chairman said 'you've got to do it, we're going to get all the players there'.
"It was nice to be thought of again in those terms but I don't really want to be running after the world champions when we've got a game on Saturday."
Gibraltar lost their first competitive international 7-0 to Poland.