Head coach Javi Gracia, whose side play at relegation rivals Bournemouth on Sunday, said: “Luis will be out for the rest of the season. I think it’s something in his ankle, a ligament.
“It’s tough for us to lose key players. I prefer to not complain. I have enough players to compete better and try to work with them and find a way to get results.”
Gracia is still waiting to learn whether USA midfielder Tyler Adams will play again this season following hamstring surgery last month and key defender Max Wober remains doubtful for the game at Bournemouth.
Gracia has come in for heavy criticism for not starting winger Willy Gnonto in recent weeks and he could return to the starting line-up at the Vitality Stadium in Sinisterra’s absence.
Italy forward Gnonto was an unused substitute against Leicester and has been named among the substitutes in Leeds’ last five matches, with his omission a source of anger and puzzlement for a large section of fans.
Gracia said: “You ask me about Willy many times and I always say the same. He’s an exceptional player with an amazing character.
“The last game I decided to play with Cree (Crysencio Summerville), but I am sure in the next games Willy will have chances to show.
“It’s something about what I think is better for the team. I choose what’s best for the team. I think both will help us for sure.”
Former Watford boss Gracia collected 10 points from his first six games in charge after replacing Jesse Marsch in February.
But only one point from his last four has seen the pressure cranked up and a growing number of Leeds supporters fear relegation.
When asked if he was worried about his own position should Leeds lose on Sunday, Gracia said: “I’m concerned about the situation of the team.
“When I arrived we were in a worse position. When we arrived we were able to get 11 points in 10 games and of course we want to get more.
“We are focused on trying our best in these five games that are left, starting from Bournemouth.”
Leeds halted a run of three straight defeats on Tuesday night, but have won only one of their last six matches and sit one point above the bottom three in 16th place.