Jara suffered the injury in the build up to Forest's Championship fixture against Barnsley at the City Ground, but Reds boss Billy Davies opted to keep the news quiet ahead of Saturday's game.
However, Davies has since revealed that the Chile international right-back will not feature again this campaign as Forest look to win a play-off place with two matches left to play.
"Jara has a knee ligament problem and will not play again this season," the Scot told the Nottingham Post.
Jara joined Forest from West Brom in January on a loan deal until the end of the season and made 17 league appearances for the Reds.
Forest are also waiting to discover the extent of Hutchinson's latest knee injury.
Hutchinson, on loan from Chelsea, has seen his season blighted by knee problems - the latest of which saw the 23-year-old forced off midway through the second half against Barnsley on Saturday.
Following the goalless home draw with the Tykes, Davies said: "Hutchinson looks as though he has picked up a problem but we don't know the depth of it yet.
"It looks as though it could possibly be tendonitis, but we are not sure.
"The boy was devastated, but I said to him that he has had a stop-start season."
Hutchinson retired from football in August 2010 because of his chronic knee problem but returned to the game 18 months later.