Keyshawn's Johnson has struck again ... allegedly.
The ex-NFL star has been hit with paternity docs by a 35-year-old woman who claims 45-year-old Key knocked her up back in 2016 -- and she's demanding child support for her 4-month-old son.
But Key says the allegations are 100% false.
According to court docs obtained by TMZ Sports, the woman has demanded a paternity test to establish Keyshawn as the father -- and once it becomes official, she wants at least $4,346 per month in support.
The rub ... Keyshawn is still legally married to another woman, Jennifer Conrad, and was at the time of the alleged conception.