The head of Nigeria's anti-corruption unit has reportedly been ordered to go on year-long study leave, in an apparent attempt to sideline him.
Nuhu Ribadu was promoted in April
Nuhu Ribadu, who has spearheaded Nigeria's attempts to combat financial crime, is involved in the prosecution of seven former state governors.
Observers say that if he is removed from his post, it will be a blow to President Umaru Yar'Adua's credibility.
The president came to power in May promising to fight rampant corruption.
Reports say Mr Ribadu was told to tender his resignation in readiness for further studies.
Nigeria's police chief Mike Okiro called a press conference to say there were no ulterior motives behind the move, and that Mr Ribadu had been ordered to attend a one-year policy and strategic studies course in central Nigeria.
The BBC's Alex Last in Lagos says that despite the official denials, the notion that Mr Ribadu may be removed from office is highly controversial and invites suspicion that the move is designed to hinder the campaign against corruption.
In the last few months the agency has arrested a number of former state governors, most recently James Ibori from Delta state: a hugely wealthy and powerful politician who was a key figure in President Yar'Adua's election campaign.
In April, outgoing President Olusegun Obasanjo promoted Mr Ribadu and gave him a new four-year mandate to co-ordinate anti-corruption work.
His critics, who saw Mr Ribadu as an ally of Mr Obasanjo, said he was being rewarded for silencing the opposition.
Chris Albin-Lackey, researcher on Nigeria at Human Rights Watch, told Reuters that if Mr Ribadu's suspension goes ahead, "the day he leaves office will be the day the credibility of Nigeria's 'war on corruption' is entirely destroyed".
The campaign group Transparency International, describes Nigeria as one of the most corrupt countries in the world.
The Economic and Financial Crimes Commission (EFCC) under Mr Ribadu has convicted over 150 persons involved in economic and financial crimes since its establishment in 2003.