Only Lara was eligible to win the vacant title after Alvarez, brother of middleweight king Canelo Alvarez, failed to make weight on Friday by more than four pounds.
The high-profile December 7 duel, dubbed 'Clash on the Dunes', will see Britain's Joshua trying to win back the IBF, WBA and WBO titles he sensationally lost to American fighter Ruiz in New York in June.
US sports broadcaster ESPN is slated to stream the fight, which will take place at an MGM property still to be named.
It's the second time Davis, 21-0 with 20 knockouts, will defend the crown he won by stopping Argentina's Jesus Cuellar in the third round in April 2018. Davis also knocked out Mexico's Hugo Ruiz in the first round last February.
Dadashev, known as "Mad Max", was unable to walk to the dressing room and was immediately hospitalised.
It made the announcement in a post dated Sunday on its official account on Chinese social media platform WeChat.
The 40-year-old Filipino legend wrote another improbable chapter in his glittering career on Saturday, with an age-defying split decision victory over the hitherto unbeaten Keith Thurman.
Pacquiao floored Thurman with an electrifying combination in the first round and remained on the front foot throughout a pulsating 12-round duel.
Filipinos from street vendors to lawmakers went wild, pumping their fists in the air during the first round of the welterweight fight as Pacquiao floored the WBA champion 10 years his junior, and went on to win by split decision.
Filipino icon Pacquiao will be climbing into the ring for the 71st time in what is seen as his most challenging contest since defeat to Floyd Mayweather in 2015's "Fight of the Century."
The 40-year-old Filipino icon clashes with Thurman at the MGM Grand in Las Vegas in what is arguably his most challenging assignment since losing to Floyd Mayweather in 2015.
Pacquiao's long-time trainer Freddie Roach said last week he would be keen for the Filipino icon to set up a rematch with Mayweather after a frustrating defeat in the first meeting.
It was a fifth successful defence of the title by Vargas, who has held the belt since defeating Gavin McDonnell in February 2017.
The undefeated Thurman puts his World Boxing Association welterweight crown on the line against the 40-year-old Pacquiao on July 20 at the MGM Grand.
The British boxer, whose parents are from Yemen, needed this victory over mandatory challenger Jimenez to put himself in position for bigger fights.