Oh, they had enough troops for Manchuria, but of course at that time what happened there wasn't all that important to the mainland, and USSR had little in the way of ability to get there anyway.
What Zhukov had shown at Khalkhin Gol, just as against Germans, was that with a significant advantage in manpower and equipment (double the manpower, 7 times the tanks) Soviets can actually beat up someone.
Japan was plenty concerned, especially remembering the last time they met USSR military. [2]
In fact, memories of that smashing were arguably the reason Japan turned east to Pearl Harbour, rather than west to Soviet Union. [3]
[1] https://www.warhistoryonline.com/instant-articles/red-army-i...
[2] https://en.wikipedia.org/wiki/Battles_of_Khalkhin_Gol
[3] https://www.goodreads.com/book/show/13102802-nomonhan-1939