Obasanjo was made the third respondent to the petition filed before the Presidential Election Tribunal in Abuja.
The protest was contained in a memorandum of conditional appearance filed before the Tribunal by Obasanjo's counsel, Malam Bello Adoke (SAN).
The memorandum, addressed to the Secretary to the Tribunal, was obtained yesterday by the News Agency of Nigeria (NAN).
Dated August 20, the document reads in part: ``Please, enter a conditional appearance for Chief Olusegun Obasanjo (the President and Commander-in-Chief of the Armed Forces) who is sued as third respondent in the above petition''.
NAN reports that the reasons for the protest had not been made available to the tribunal.
However, they are expected to be contained in a subsequent motion yet to be filed by Adoke.
It will be recalled that the tribunal, presided over by Justice James Ogebe, had ordered service of the petition on Obasanjo through a substituted means of publishing it in a National Daily.
The order of the court was sequel to a complaint by Buhari's counsel, Chief Mike Ahamba (SAN) that it was difficult to serve the petition on the former President.
In the petition, Obasanjo was specifically alleged to have used his position to deploy the Police, Army and other security agencies who masterminded the rigging of elections in favour of PDP.
Meanwhile, Ahamba has said that he needs to certify over 50,000 pages of document obtained from INEC to prove his case.
The lawyer alleged that INEC was curtailing prompt certification of the documents by posting only a staff to do the bulk job.
Ahamba appealed to the tribunal to intervene by directing INEC to deploy more staff to handle the job in good time.
The tribunal, however, declined granting the order against INEC but advised the body to assist the lawyer to that effect.
The petition has been adjourned till September 3 for further hearing.
In the petition, Buhari and his running mate, Chief Edwin Ume-Ezeoke, are asking the tribunal to nullify the election of President Umaru Musa Yar'adua.
The petitioners, among other reasons, contended that the election was marred with violence, rigging, malpractice and irregularities.