Mr Yeddyurappa says he knows nothing about the posters.
Two days before Narendra Modi hits town for a mega rally in Bangalore, many posters have sprung up featuring former Karnataka Chief Minister BS Yeddyurappa and Mr Modi, the BJP's prime ministerial candidate, together.
Mr Yeddyurappa is a Modi fan, but he is no more part of the BJP, having split a year ago with his party of 40 years, to float his own political outfit, the Karnataka Janata Party, made up largely of BJP rebels.
The posters have been put up by a KJP member, but Mr Yeddyurappa says he knows nothing about them.
Ever since Mr Modi was named the BJP's presumptive PM, there has been speculation that Mr Yeddyurappa could merge his party with the BJP. Mr Yeddyurappa has repeatedly ruled out a merger but has said his party will be happy to support a BJP led by Mr Modi.
BJP leaders in the state refuse comment saying any decision to re-induct Mr Yeddyurappa into the party will be taken only by the party's central leadership.
Mr Yeddyurappa is a powerful leader from the influential Lingayat community and is credited with having won the BJP its first and only government in south India when it had won the Karnataka Assembly elections in 2008.
The 70-year-old had to step down in the middle of his term because of corruption charges and held the BJP to ransom for many months before finally walking out for not being given a prominent party position.
In the elections held this year, the Congress trounced a fractured and struggling BJP and Mr Yeddyurappa failed to make a dent with his KJP.
Even star campaigner Narendra Modi had failed to lift the BJP's chances in the state, despite drawing large crowds in Mangalore and Bangalore, when he visited the state in April just before the Assembly elections.
For his Bangalore rally on Sunday, the BJP claims nearly three lakh people have bought tickets at Rs 10 each to watch Mr Modi, now campaigning for general elections due by May.
The party has reportedly spent Rs 20 crores on Mr Modi's event at the Palace Grounds, a large public space in the heart of the city.