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Donald Trump's work in China isn't done yet ...

The mother of an ex-Canadian Football League player -- who's now locked up in China -- is hoping POTUS can work his magic again and bring her son home, too.

30-year-old Wendell Brown ﻿-- a former LB at Ball State -- was coaching an American football team in Chongqing, China last year when he was involved in a bar fight and arrested.

Brown claims he was attacked and was forced to defend himself. He claims several witnesses corroborate his story.

Still, he was locked up in a Chinese prison and put on trial. Brown is still behind bars while waiting on the verdict ... despite the fact the trial concluded back in June.

Now, Brown's mother Antoinette says she hopes President Trump will get involved the same way he did when LiAngelo Ball and the UCLA basketball team needed his help.

"My message to President Trump is I pray you have enough compassion to help me with my innocent son that's detained in China."

Antoinette says her son has never been in trouble with the law before -- and she wants him to get home to his 10-year-old son who misses him.

"It's been hell," Antoinette explains. "My son is like one of my closest friends."