The meeting, at the MNS chief's Dadar residence, comes after BJP announced support for an Independent candidate.
After the meeting, Dhananjay denied that he met Raj in connection with the bypoll. "It was a courtesy visit," he said.
The bypoll is being held to fill the vacancy caused by his resignation as BJP MLC elected by members of the Legislative Assembly.
Dhananjay resigned as a member of the Upper House on July 2 and joined NCP, which is part of the Congress-led ruling coalition in the state. His term of office would have, in the normal course, ended on July 7, 2016.
However, the two withdrew from the fray and were present at a media briefing by Gopinath Munde later where he said BJP has decided to back the candidature of Prithviraj Sambhaji Kakade, who filed his nomination papers as an independent candidate.
The electorate for this constituency comprises 288 MLAs of the Lower House. Congress has 82 MLAs, NCP has 62, BJP 46, Shiv Sena 44, MNS 12 while small parties and independents make up 39 members.