According to the police report ... the outrageous call, made back in January, came from someone claiming to work for Williams' production company. The caller believed Kevin was slipping Wendy something harmful, and he or she wanted cops to check on her.

The report says 2 officers went to Williams' New Jersey residence and were greeted by Hunter, who was hesitant to let them in for the welfare check because he said Wendy was sick and recovering from a health problem.

Cops say they explained to Hunter they were required to speak with Williams due to the anonymous call. When he allowed them to enter, they found Williams in bed "with the blanket covering from neck to toe."

According to the report ... one of the officers asked Kevin to leave the bedroom so they could talk to Wendy alone, but he didn't want to leave her side. As for the health problem she had -- Wendy told cops she was recovering from a broken shoulder.

An officer eventually asked her if there was any truth to the anonymous tip she was being poisoned, and Wendy responded with something like ... "Well, I'm very popular." When the cop repeated the question, the report says she became tearful, but denied there was any truth to it.

The cops left after Wendy told them once more she was okay.

As we reported ... Williams filed for divorce from Hunter this month amid cheating rumors, and just weeks after she returned to her show and announced she was living in a sober home and getting treatment for addiction.

She was on hiatus from her show at the time cops performed that welfare check.