Forest wanted to buy the right-back but could not reach an agreement with his club, Le Havre, over a fee.Instead, they have paid a loan fee of pounds 100,000 and have a first refusal option on him.
Dave Bassett, the Forest manager, said: "We couldn't reach an agreement over a fee but this is the next best thing."
Forest have been pursuing Louis-Jean' since he completed a trial at the City Ground last month and he joins his fellow countryman, Jean-Claude Darcheville, at the club.
Darcheville, who scored his first Premiership goal in a 2-1 win at Southampton on Saturday, is also on loan for the season from Rennes.
The Chelsea coach Graham Rix has offered the Stamford Bridge veteran Steve Clarke his best wishes, as the former Scottish international considers joining the coaching staff at Newcastle United.
Clarke is wanted by the former Chelsea player-manager Ruud Gullit as part of his management team at St James' Park. Rix said: "We wanted to use him in a year or two's time, in some capacity, in the club and we thought it would be an ideal situation with him still being available as a player, being on the inside and learning management skills.
"But this opportunity has come up and you know he has got to go. If he has got anything about him or any ambition - which he has - then he has got to accept it.
"It's a loss for us, there is no doubt about that. He has done great service for us, I don't think that is describing it well enough what he has done for us over the last 12 years."Reuse content