Dear Navdeep,
This is a very sensitive issue. She has not explained in detail what kind of problem she is facing from him. Her explanations such as "I'm not comfortable with him" is a very vague description deserving followup action. However, In the circumstances explained, in the absence of a written complaint, HR cannot take any formal action on record. However if it is possible U can check with other colleagues friendly with U, secretly about his nature and if at all he had behaviourial problem with others too. This is necessary to make sure within yourself some problem is there prima facie. If so, you can talk to him personally in a friendly atmosphere and diplomatically push thro' such opinions are going round in the co. without mentioning her name. If he is apologetical U may inform her accordingly. If it is not working out and if he becomes aggressive U have to make it demi-official, recording her version and send a secret note to your counter part in his dept.for further action. It's all the more necessary for U to bring it to the logical conclusion.
Nevertheless it would be premature to presume presence of a sexual harassment between them. We also can go thro' similar topic was discussed in this forum.
https://www.citehr.com/12027-sexual-...ace-india.html
kumar.s.