Oldham have publicly complained that they will lose the player for nothing if he moves to Scotland, while an English club would pay compensation.
Thompson told BBC Sport: "We're definitely interested in the player.
"But we are staying within the rule book and matters should progress soon."
English clubs would be required to pay compensation because Porter, who scored 21 goals in League One last season, is under 24.
However, that would not apply to a cross-border transfer for the 23-year-old striker.