The 31-year-old adds to Alex McLeish's attacking options after moving from The New Den and comes into immediate contention for a starting spot against Watford this weekend.
Adding a different, more physical, option for McLeish, the Forest boss is also looking at the type of player who can provide Henderson with the service he will thrive on with Birmingham's Chris Burke still the most likely option.
Former Reds boss Sean O'Driscoll, meanwhile, is looking to tie up a deal with his old club for versatile defender Brendan Moloney.