5/31/19 -- Two other former UCLA players -- OL Zach Bateman and OL Poasi Moala -- have joined Lopez's lawsuit against the school and Mora.

"Each of these young men suffered serious, but significantly different injuries, while they were teammates at UCLA," said their attorney, Pamela Tahim Thakur.

"While the lawsuits involve many of the same facts, each case is distinct in its own way. But what they all have in common is the pattern of brutality and intentional disregard for player health and safey by Coach Mora and his staff at UCLA."

10:30 AM PT -- A spokesperson for UCLA Athletics released a statement to TMZ Sports ... saying, “While we cannot comment on the specific details of a pending lawsuit, we want to make it clear that the health and safety of our student-athletes is UCLA’s top priority."

"We strongly deny and will defend ourselves against the allegations made in the lawsuit. We handle every injury with the highest standard of care, and take potential head injuries very seriously. As one of the world’s leading research institutions, and a partner in the largest-ever concussion research study conducted by the U.S. Department of Defense and NCAA, we believe our concussion protocol is among the strongest in the country."

"Our team physicians and sports medicine staff work hand-in-hand on diagnosis, monitoring and treatment, and they are the only individuals who determine when a student-athlete is cleared to participate in their sport; coaches are not involved in these decisions.”

Former UCLA coach Jim Mora's practices were so rigorous -- and his concussion protocol was so flimsy -- an ex-OL tried to kill himself ... so claims one of Mora's former top recruits in a new lawsuit.

John Lopez -- a 6' 5", 305-pound offensive lineman -- says repeated concussions he suffered during Mora's practices led to his suicide attempt back in 2016.

Lopez claims after being recruited by Mora to UCLA ... he almost immediately suffered his first-ever concussion at the Bruins' August 2013 training camp in San Bernardino.

Lopez says Mora and his staff didn't take the proper steps to safely return him back to the field ... and rushed him back into practice.

In fact, Lopez says he was ridiculed for being injured ... and alleges one of Mora's coaches even made up a special drill where other players were encouraged to "f*ck him up!"

Lopez says the following year -- at the start of his sophomore season -- at UCLA's August 2014 training camp in San Bernardino ... he suffered a second concussion in an on-field drill.

John claims he was rushed back to the field once again ... and says the drills he was put through in his return were "unnecessarily brutal."

Lopez says a year later -- in December 2015 of his junior season -- he suffered yet another head injury ... and his post-concussion symptoms were so bad, he was forced to medically retire from the team.

But, John says the damage the brain injuries did were already crippling ... saying he suffered from short-term memory loss, depression and "drastic changes in his demeanor."

Lopez says it all came to a head in the fall of 2016 ... when he attempted to kill himself by overdosing on a combination of over-the-counter and prescription medications.

Lopez says he was able to inform family members and friends of his suicide attempt ... and they were able to save his life at the emergency center at UCLA's medical center shortly after.

John is now suing Mora, members of his staff, UCLA and the NCAA ... claiming they didn't do enough to protect him both before he suffered concussions and afterward.

Lopez is now seeking more than $15 MILLION ... saying the trauma he suffered during his time at UCLA is preventing him from finishing school and is causing him emotional pain, suffering and distress.

We've reached out to UCLA for comment -- so far, no word back.