The midfielder was left out of Carlisle's side on Monday as they crashed to 6-1 defeat at Wrexham. United manager Roddy Collins gave a stomach bug as the reason for his omission, but rumours suggest the pair have fallen out.
With this revelation and Carlisle sitting just a point above the relegation zone, the likelihood of Green's loan deal being extended to a permanent move is unlikely.
After paying out £150,000 for the player, City won't be willing to let him go for free, so he could return to the Tigers squad for next season.
Manager Peter Taylor said: "At the end of the day, if Stuart comes back to us we know he's a good player and it's up to him to prove it if he decides to stay at Hull."
Grass No Longer Greener?
He added: "But you never know, all of a sudden Carlisle might come up with the money and Stuart might sign there. But if he doesn't he will be treated the same as everybody [else]."
Elsewhere, City's championship-winning Reserve side ended the season with a 0-0 draw against Boston yesterday. They will contest the League Cup Final against Doncaster Rovers in pre-season.
Elsewhere, City's championship-winning Reserve side ended the season with a 0-0 draw against Boston yesterday. They will contest the League Cup Final against Doncaster Rovers in pre-season.