Benitez, who played 58 times for Ecuador, was the son of Ermen Benitez, one of his country's all-time leading goalscorers.
El Jaish, who signed Benitez only three weeks ago, confirmed his death on their website (www.eljaish.com).
Some reports said he died in a car crash, others that he suffered a heart attack after a training session.
"The club would like to offer its sincere condolences to the family of the player," the statement said.
"Benitez had recently joined the club from Club America for three seasons.
"The player participated for the first time with the team during yesterday's match against Qatar Sports Club in the Sheikh Jassem Cup without complaining of any health problems.
"His sudden departure is a big shock for each member of the technical and administrative staff. He was a player that over the short period he was here was regarded for his high moral character."
Benitez spent the 2009-10 season on loan at Birmingham City in the English Premier League and the club said they would mark the player's death ahead of Saturday's Championship match against Watford at St Andrew's.
Benitez's former Birmingham team mate Craig Gardner, now at Sunderland, tweeted: "Cannot believe Christian Benitez has died. I had the pleasure to play with him. He was a top bloke. My thoughts go out to his family."
Benitez, also known as 'Chucho', scored four goals in 36 appearances during his time in England and came to prominence during the 2006 World Cup in Germany.
(Reporting by Mike Collett, editing by Ed Osmond)