The 26-year old has started all three Premier League games for Steve Clarke's side so far this season, having netted eight times during the last campaign.
Long had only just linked up with Giovanni Trapattoni's squad ahead of their World Cup qualifier against Sweden at the Aviva Stadium on Friday night, but it is suggested that Hull have swooped with a view to completing a late deal.
Despite bringing in no fewer than 10 new faces to the KC Stadium this summer, Steve Bruce has been linked with a move for a host of strikers in recent weeks, including Arsenal's Nicklas Bendtner and former West Ham forward Carlton Cole.
Long played the full 90 minutes in Sunday's 2-0 defeat at home by Swansea, and he has been unable to prevent his side from sitting at the foot of the table.
Hull, who have already boosted their attacking options with the signings of Yannick Sagbo, Danny Graham and George Boyd this summer, have taken three points from their opening three games since securing a Premier League return.