David Hess stepped away from Major League Baseball in 2021 after doctors diagnosed him with cancer.
On Friday, the pitcher revealed his battle with the disease is not over.
"The last couple weeks have been a whirlwind for us with this cancer journey that seems to never want to end," he posted to social media Friday.
Hess noted that he was diagnosed with a form of cancer known as angiosarcoma.
"We found out that inside my tumor was [a] very rare and very aggressive type of cancer called angiosarcoma. Along with that discovery, lung nodules have popped up that we aren't sure what to make of yet."
The 29-year-old said he will undergo surgery next week to biopsy the nodules. Doctors will perform a separate procedure to remove the tumor.
Hess will also undergo chemotherapy.
"I will fight like hell and do whatever is needed for a cancer-free prognosis at some point," he wrote in a social media post.
Chicago White Sox pitcher Liam Hendriks and wife Kristi are among the donors who have contributed to an online fundraiser in support of Hess and his wife Devin.
Hendriks was diagnosed with non-Hodgkin lymphoma in 2022. He rang the "victory bell" at his final chemotherapy session April 5.
Hess was diagnosed with a rare form of cancer known as a germ cell tumor, which doctors discovered shortly after the 2021 baseball season. He underwent treatment and was cleared to return to normal activity in early 2022.
Last February, he reported to spring training with the Tampa Bay Rays before pitching in the minor leagues at the Triple-A level. He finished the minor league season with a 2-1 record and a 13.06 ERA in eight relief appearances.
Hess has a career record of 6-22 with a 6.25 ERA. Aside from his time in the Rays organization, Hess spent three seasons with the Baltimore Orioles and had a stint with the Miami Marlins.