When Tesla announced the Gigafactory 3 in Shanghai, China, it said that the battery modules/packs would be produced using lithium-ion cylindrical cells (21700 type) from various suppliers, "including Panasonic".
That still might be the case, but according to Panasonic CEO Kazuhiro Tsuga, there are currently no plans for a new battery plant for/with Tesla in China:
"“We don’t have any plans at the moment to set up a production site in China for Tesla’s Chinese business,” CEO Kazuhiro Tsuga told reporters at a strategy briefing on Friday.
“It is up to Tesla to decide whether it would use Chinese-made batteries from other manufacturers or get batteries from our Gigafactory 1 (in Nevada),” he said."
The main reason behind the "dream-team" possibly splitting ways is the lack of profitability of the battery cell production at the Tesla Gigafactory 1 in Nevada.
The right word for Panasonic now is "caution":
"Tsuga earlier this year admitted he underestimated risks associated with Tesla."
Supply from Gigafactory 1 sounds like a bad idea and might be considered probably as a short term solution. Panasonic has battery plants in Japan (although it's only ready for 18650 type cylindrical cells) and in China (in Dalian and Himeji, although it's set up for prismatic cells).
There is also an option to launch battery cell production on its own (using some new tech from Maxwell).