The former president said he couldn't attend the event becuase he's currently not in the country.
Shortly after President Buhari presented the title to Abiola's son, Kola, and apologised to the family for his death, it was announced at the investiture that Obasanjo had sent an apology for his absence.
According to a statement he addressed to Buhari and Nigerians, Obasanjo said he failed to show up for the event because he's away in Norway attending the 2018 Africa Food Prize which honours achievements in African agriculture.
The statement further noted that he prayed and wished "Mr President and the country a very successful investiture ceremony".
Obasanjo has come under a lot of flak since Buhari announced his decision to award Abiola the GCFR title in recognition of his contribution to the nation's democratic history.
Abiola was the presumed winner of the June 12, 1993 presidential election which was annulled by then-military Head of State, General Ibrahim Babangida. After Abiola refused to give up his mandate, he was imprisoned in 1994 where he died in custody under suspicious circumstances on July 7, 1998, four years after his arrest.
Many have questioned why Obasanjo failed to honour Abiola's memory while he was president between 1999 and 2007, especially since they were both from the south west region and it has been widely believed that his electoral victory in 1999 was an attempt to placate the region for Abiola's death.
Despite Obasanjo's official reason for missing the investiture ceremony, the former president's absence has been speculated by some to be due to Obasanjo's recent public clash with Buhari.
In a statement released by his spokesperson, Kehinde Akinyemi, on June 8, 2018, Obasanjo alleged that Buhari's administration has an active plan to indefinitely detain him by using false witnesses and documents to frame him. The former president alleged that the current witch hunt against him is fueled by his wave of criticism against the president.
Obasanjo's war of words with Buhari notably started when he publicly condemned the president's administration in January and asked him to not seek re-election in next year's election.
In that 13-page statement titled, "The Way Out: A Clarion Call for Coalition for Nigeria Movement", Obasanjo also expressed his lost hope in the ability of the ruling All Progressives' Congress (APC) and the People's Democratic Party (PDP) to provide Nigeria with the initiative it needs to progress.
He subsequently launched the Coalition for Nigeria Movement (CNM) which he said would be a movement of all well-meaning Nigerians that will engage in democratic practices that will drive Nigeria forward and be a source of hope for all Nigerians. That movement has recently adopted the African Democratic Congress (ADC) as its political platform to install a new political class in the 2019 general elections.
With Obasanjo constantly criticising Buhari since that January statement, the most high-profile clash between the two happened in May when the president raised questions over the $16 billion allegedly spent on power projects during Obasanjo's administration.
While speaking at the Presidential Villa on May 22, 2018, Buhari remarked, "One of the former Heads of State was bragging that he spent more than 15 billion USD on power in Nigeria. Where is the power?"
In response to the accusation, Obasanjo fired back later that day, saying that Buhari was ignorant on the subject for re-echoing an unsubstantiated allegation that has been proven false.