By TMZ

Former light heavyweight champion Sergey Kovalev has been charged with felony assault for allegedly punching a woman in the face back in June -- but he claims he's not guilty ... TMZ Sports has learned.

Here's what we know ... the Russian fighter was arrested in Big Bear, CA on June 9 after a woman told police the feared puncher struck her in the face, causing serious injuries.

Sources connected to the case tell us ... the woman is claiming Kovalev had hit on her at a party earlier in the evening but rejected his advances. She claims Sergey and a friend followed her back to her cabin and that's where the alleged attack occurred.

We're told the woman claims she suffered major injuries including a severely broken nose, a concussion and a displaced disk in her neck.

Cops tell TMZ Sports ... they began searching for Kovalev immediately and arrested him a short time later.

He was charged with assault by means of force likely to cause great bodily injury -- which carries a maximum sentence of 4 years in prison.

Kovalev appeared in court and entered a not guilty plea.

What's interesting ... Kovalev fought Eleider Álvarez in August -- just 2 months after the arrest -- and lost in a shocking upset.

Kovalev is due back in court in March. He also has a rematch with Alvarez lined up for Feb. 2.

We've reached out to Kovalev for comment -- so far, no word back.