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During this global pandemic, Mike and his family had many discussions about playing this season. They took countless factors into consideration, many of which are personal to him and his family. After thorough consideration, he has chosen to opt out of playing in 2020. This was not an easy decision for Mike. He wishes the best of luck and health for his Diamondback teammates this season and he’s looking forward to 2021.
For the aforementioned opt-out group, the decision of whether or not they would receive salary or service time will be left up to each individual team. High-risk would include people who have heart disease, lung disease, cancer, high blood pressure, or diabetes.

Leake, 32, will be a free agent following the 2020 season if Arizona declines his million 2021 contract option. This is the explanation for his opt out from his agent, Danny Horwits, via Passan:

Leake was included on the Diamondbacks’ initial 60-man roster for the 2020 season, and he would likely be fighting to earn a rotation spot. While Leake is the first known player to opt out of playing this year, he’s likely not going to be the last given the health risks involved with playing during the coronavirus pandemic.
As part of MLB’s return-to-play plan, high-risk players — those with pre-existing medical conditions or compromised immune systems are at a higher risk for severe illness from COVID-19 — can decide to opt out of the 2020 season at any point and they would receive both their full salary and service time for the season. It’s unclear whether Leake falls under that category. He finished the 2019 season with an 12-11 record, 4.29 ERA and 1.289 WHIP in 197 innings. Leake joined the Diamondbacks at last year’s July trade deadline from the Seattle Mariners. 
MLB and the MLBPA have agreed on a “spring” training that starts July 1 and a regular season that begins July 23.
Major League Baseball is planning to return to play in less than four weeks. As part of the MLB Players Association (MLBPA) and league’s coronavirus (COVID-19) health and safety protocols, any MLB player can decide to opt out of the 60-game 2020 season. Arizona Diamondbacks right-hander Mike Leake is the first to publicly announce his opt-out decision.