The former chief minister indicated the Shiv Sena can have a formal alliance with the Congress, subject to approval by his party's central leadership.
"The Shiv Sena is in power with the BJP today and if it separates and wishes to come with the anti-BJP parties, we would think and a proposal (for alliance) may be sent to the high command in Delhi," he told reporters.
Mr Chavan was in Aurangabad to attend a party convention.
The Sena, the oldest constituent of the NDA, recently announced that it would contest the 2019 Maharashtra assembly and Lok Sabha elections on its own.
The Uddhav Thackeray-led party is currently part of the BJP-led governments at the Centre and in Maharashtra.
Mr Chavan said all parties which are against the Sangh ideology should come together to defeat the BJP.
"All parties which share anti-Sangh ideology should come together in the forthcoming elections. This would make it easy to defeat the BJP," he said.
Replying to a question, he said in the 2014 Lok Sabha elections, the Shiv Sena was in alliance with the BJP but it fought the assembly polls in Maharashtra, held later the same year, alone.
"Some days ago, the Shiv Sena declared it would go alone in the upcoming elections.
"But I personally feel Prime Minister Narendra Modi, Maharashtra Chief Minister (Devendra Fadnavis) and other (BJP) leaders would not let that happen," Mr Chavan said.
However, state unit Congress president Ashok Chavan said there was no possibility of a tie-up between his party and the Shiv Sena, considered ideologically rival outfits.
"There are no chances of the Congress and the Sena joining hands in Maharashtra in the coming days," he said in Satara in Western Maharashtra.