"My personal opinion is that outside support does not work. The largest party cannot be out of the coalition....does not work," the party General Secretary said.
"Outside support is something which is impractical....too utopian. It has to be a pragmatic policy and working of a coalition has to be that everyone has to be accountable in the Cabinet. People from outside....I think....it does not work."
On the party extending outside support to the United Front government in 1996, the former Madhya Pradesh Chief Minister said, "It didn't work."
"Well, I would not say it", Singh said when asked if it was a mistake on the part of Congress to do so at that time.
"It may have been the right thing to do at that time but certainly it didn't prove to be the right thing to do."
The Congress leader's remarks come after Maharashtra Chief Minister Prithviraj Chavan last week said his party could form the next government by joining hands with "the Third Front", while Union minister Salman Khurshid said they could consider extending support to it or taking its help to form the government if necessary after the Lok Sabha polls.
Union minister Jairam Ramesh said on Sunday he is not in favour of extending outside support to the Third Front dispensation if numbers don't stack up for NDA.
Rather, he hinted he wants his party to join the government for stability if it comes to that.
Meanwhile, Singh sought to junk the poll surveys that projected only around 100 Lok Sabha seats for Congress.
"It's not for the first time poll predictions are going against us. Even in 2004, the poll predictions were that NDA is going to sweep the polls....India Shining Campaign....even in 2009 the polls had predicted an NDA victory," he said.
"I dont know why pollsters are very favourable to NDA and not very favourable to us. But we have proved them wrong in 2004, 2009 and inspite of the blitzkrieg of publicity by Narendra Modi for his own benefit, we are going to do much better than what pollsters are predicting," he added.