Weili Zhang -- the reigning UFC strawweight champ -- says Joanna is washed up and does NOT deserve a shot at her belt, despite beating Michelle Waterson this past weekend.

Remember, Zhang won the title by DESTROYING Jéssica Andrade in 42 seconds when they fought back in August ... and now she's ready to defend her belt.

Joanna told TMZ Sports she deserves a title shot -- but Zhang adamantly disagrees, saying the Polish superstar's best days are behind her.

"I don't think shes the fighter that she used to be," Zhang says ... "She's not in the condition she used to be. I'm not very interested."

Joanna went on an impressive 14-0 run to start her MMA career -- but lost 3 out of her last 5 ... twice to Rose Namajunas and once to Valentina Shevchenko.

In fact, Zhang says she's WAY more interested in moving up a weight class and fighting Shevchenko for the Flyweight belt than taking on Joanna.

"I want to fight the best," Zhang says ... "Right now I think Valentina is one of the best."

Zhang says she'd also consider a fight against Rose ... but she hasn't made up her mind yet.

There's more ...

Zhang also weighed in on the political drama between her home country, China, and the United States ... saying she hopes she can help repair relations through sports.

Speaking through a translator, the 30-year-old said ... "Hopefully I can be the bridge between all countries and the U.S."