The 22-year-old joined the Gers on a season-long loan on the final day of the transfer window, and could face Celtic in the Old Firm clash.
Rangers skipper Lee Wallace limped out of the 2-2 draw against Patrick Thistle with a groin injury, and John replaced him in the first half.
Wallace is a major doubt for the match, and should he fail to recover, John will get the nod to face Celtic.
Celtic were absolutely dominant in this fixture last season, with Patrick Roberts (on loan from Manchester City) terrorising Rangers defence, and especially rookie Ibrox full-back Myles Beerman.