D-backs reliever Brad Ziegler was one of the first to break the news of Weiner's passing. A player representative since the start of the 2009 season, Ziegler formed a close relationship with Weiner.
"Lost a great friend today," Ziegler wrote on Twitter. "Michael Weiner's body finally succumbed to cancer. One of the best leaders & men I knew. Prayers for his family."
Those sentiments were echoed by players across the league, many of whom also took to their Twitter accounts to show their appreciation for Weiner.
"My prayers go out to Michael Weiner and family," wrote Marlins player rep Steve Cishek. "This guy fought hard for us players and he will never be forgotten. He will be missed."
"My deepest condolences to the Weiner family tonight," wrote Tigers pitcher Max Scherzer, the 2013 American League Cy Young Award winner. "He had a special and unique way to connect to everybody that never will be forgotten."
"[A]lso saddened to see the passing of @MLB_PLAYERS Michael Weiner -- he was truly an inspiration to us and a stronger man the rest of us," wrote Angels pitcher C.J. Wilson.
While players often are lauded for staying on the field despite injury, many recognized what it took for Weiner to continue with his work under much more dire circumstances.
"Michael Weiner worked even thru his sickness," wrote Pirates outfielder and National League Most Valuable Player Andrew McCutchen. "He didn't look at it as an excuse to quit. He never gave up on us even when at his worst. You truly will be missed. Prayers go out to his friends and family. An amazing person to us all."
It wasn't only Cy Young winners and MVPs who appreciated Weiner. He also touched lower-profile players such as veteran reliever Clay Rapada, who appeared briefly for the Indians this season.
"I carry a burden heart for Michael Weiners family today," Rapada wrote. "Was so helpful and informative to journeymen like myself…" @MLB_PLAYERS #thankful"
"You could tell that Michael Weiner really cared about us," added free-agent reliever Joel Hanrahan. "He really wanted to know how you were. He'll be missed a lot. Amazing person."
Catcher Jason Castro, the Astros' player rep, told MLB.com that he had been to dinners with Wiener during Spring Training, giving him a chance to get to know the man a little outside of baseball.
"He was as dedicated as they come, and to have someone like that running the organization, it makes you feel good and confident you're in the best of hands," Castro said. "Obviously, that staff working around him has been great, but he's definitely going to be hard to replace, and our thoughts and prayers are with his family and loved ones, and it's a difficult thing to deal with. I think it's more about remembering everything he brought to the game and the legacy he'll leave behind. He really will never been forgotten for everything he's done for baseball."
"It's a sad day for baseball, that's for sure," Rangers player rep Derek Holland said. "We're going to have to talk and see who we get to replace him, but at the moment, it's a time to reflect on his passing. The guy did a lot of great things for the baseball community as a whole."
The players weren't the only ones to express their feelings about Weiner. One of those to release a statement was Commissioner Bud Selig.
"All of Major League Baseball mourns the loss of Michael Weiner, a gentleman, a family man, and an extraordinarily talented professional who earned the trust of his membership and his peers throughout the national pastime," Selig said. "Our strong professional relationship was built on a foundation of respect and a shared commitment to finding fair solutions for our industry. I appreciated Michael's tireless, thoughtful leadership of the players and his pivotal role in the prosperous state of baseball today.
"Michael was a courageous human being, and the final year of his remarkable life inspired so many people in our profession. On behalf of Major League Baseball and our 30 clubs, I extend my deepest condolences to Michael's wife Diane, their three daughters, his colleagues at the MLBPA and his many friends and admirers throughout the game he served with excellence."
Former MLBPA chief operating officer Gene Orza issued the following statement:
"Right now, tears are everywhere at the loss of Michael. In many cases, they are shed by those who only knew him in passing or on the margins, but still could sense how special he must be, and how unfair it is that he be taken this young. And they are right. He was special, and it is unfair. For those of us who worked alongside him in the offices of the Players Association, there is nothing less than a hole in our hearts right now. We all loved him so very much.
"We and Michael shared our lives together. And throughout he was ever kind and understanding, never impatient or disrespectful, constant in his friendship, concerned beyond compare, and always, always, brilliant, like a diamond or a star. Yes, he was nothing short of a star in our lives. He shines elsewhere tonight, but to those of us who really knew him we are grateful he once shone upon us."
Added Dodgers president Stan Kasten: "I am deeply saddened by the passing of Michael Weiner, with whom I had the pleasure of working for many years. I had so much respect for him and admired his leadership of the players and Players Association. He was truly a great individual, a brilliant lawyer and a thoroughly decent person. All of baseball, labor and management, has suffered a great loss. Michael was always viewed as the path to a reasonable resolution. He will be missed. The Dodgers and I send our deepest condolences to Michael's family."
Angels general manager Jerry Dipoto echoed Kasten's sentiment.
"Michael Weiner was a great guy, tremendous person," Dipoto said. "That's a great loss for baseball players, baseball in general. I know all the folks at MLB, in and around the league, respect him a great deal. It's a very sad story.
"Michael did a lot for relations between the league and the players, and again, just a great guy, a family man, a super human being. That's a tough loss for everybody. Really my heart goes out to his family, to everybody involved. I know there are so many players through the years that Michael built close relationships with. He'll be missed."