The 28-year-old Jamaican forward - who cost the Championship club £3million from Ipswich four years ago - was the subject of a three-month loan to City.
Forest said a deal with an unnamed League One side fell through at the last minute, with the Tigers reported to be that club. However, a statement on Hull City's official website says that is "not the case".
Hull City Online learns though that Johnson is one of a number of forwards Peter Taylor is watching, along with Southampton's Dexter Blacklock, Colchester's Craig Fagan and Everton's Nick Chadwick.