Villa boss Paul Lambert confirmed the news on the club website.
Antonio is struggling with his hamstring at the minute. He'll be a few weeks out.
The Spaniard has taken to the Premier League like a duck to water since his summer move from Sevilla and his absence will only add to Villa's defensive woes.
The Birmingham-based side set an unwanted Premier League record of 26 matches without a clean sheet during September. Villa finally managed a shut-out in the clash with Norwich, but the baron run stretched back to mid-way through last year's disastrous campaign.
Villa have kept just two clean sheets in their last 31 fixtures.
The 22-year-old left-back has been a key figure for Villa this season, and not just in defence—he scored Villa's third goal in their impressive opening day victory over Arsenal at the Emirates.
“Tony Moon,” as he's referred to by the Villa faithful, not only provides a stellar defensive service in Villa's back-line but is also adventurous in his attacking efforts.
Spanish in every sense of the word, Luna's endeavour when getting forward is second-to-none, and he offers more than adequate support to Villa's midfield.
The hole that he will leave on the left side of Villa's defence will feel gigantic when the claret and blues travel to East London this weekend. Paul Lambert simply does not have an suitable replacement.
Joe Bennet, who was Villa's first-choice left-back last season, has also been ruled out of the clash with the Hammers—though many Villa fans will see that as a blessing in disguise. Bennett's few performances this season, as well as his 25 last, have fallen incredibly short of what is expected of a Premier League left-back.
Lambert will more than likely be forced into playing a centre-half in a position of which Luna has made his own. The term “square pegs in round holes” comes to mind.
Either Nathan Baker or Ciaran Clark will surely be given the nod, with the other probably playing in their more comfortable central defensive role.
Both Baker and Clark have previously stood-in on the left side of Villa's defence, but in no way are they left-backs. Though both solid at the heart of defence, they each look out of place when playing anywhere other than in that position.
According to Squawka, Luna wins 65 percent of his duels and makes an average of six important defence actions each and every game for Villa. The Spaniard has also created four goal scoring opportunities for his side this term.
Luna has made such impact in the nine games he has played so far that his team-mates have spoken of their admiration for the 22-year-old.
Villa's utility man Leandro Bacuna, who replaced right-back Matthew Lowton in Villa's side following Lowton's poor start to the season, admitted that he can learn a lot from Luna.
Speaking to the Birmingham Mail's Matt Kendrick, the Dutchman said:
I’ve started to look at him more now as I’m not originally a full-back but I’m playing there at the moment. I think I can learn from Antonio.
He is going up and down all the time – always attacking and defending. I will keep improving my own game and maybe I can learn from him.
Villa face West Ham and Cardiff during the next fortnight and will need to start picking up points against teams in-and-around them in the Premier League if they're to avoid another season like the last one.
But with Luna watching from the sidelines, the chances of Villa adding to their desperate tally of clean sheets this season looks incredibly optimistic.