The right-handed pitcher revealed the news on his social media page Sunday -- saying docs recently discovered he had non-Hodgkin's lymphoma. He went on to say he'll begin medical care to try to eradicate it all on Monday.

The 33-year-old, though, vowed to beat it ... saying he's going to use "the same determination I have used when facing other obstacles in my life."

"I am confident that I will make a full recovery and be back on the mound as soon as possible," Hendriks said.

"I know with the support of my wife, my family, my teammates and the Chicago White Sox organization, along with the treatment and care from my doctors, I will get through this."

Several MLB stars commented on three-time All-Star's post ... including future Hall of Famer Miguel Cabrera, who left praying hands emojis.

Hendriks has been in the major leagues since 2011, but has blossomed into one of the game's best just recently. He had a breakout year with the Oakland A's in 2019 -- and has gone on to become one of the most reliable ninth-inning guys in baseball since.

The White Sox -- who signed Hendriks to a 3-year, $54 million contract in 2021 -- said Sunday night they plan to help the pitcher on his journey to recovery ... adding they're "optimistic he will pitch again for the White Sox as soon as viable."