The 76-year-old head of state was elected in 2015 on a promise to end the Islamist insurgency, which has killed more than 27,000 people since 2009 and left 1.8 million homeless.
But as Buhari seeks a second term in elections next month, a wave of attacks, including against military bases, has undermined his repeated claim that the group is virtually defeated.
Soldiers have also complained that Boko Haram fighters are better armed and that morale is low, particularly because of a lack of rotation and support.
In a recorded interview broadcast late on Monday on Arise TV, Buhari conceded that troops had come under pressure from the Islamists’ guerrilla warfare.
Buhari, a former army general who became military ruler after ousting the elected government in a coup in 1983, said the “question of morale is correct”.
Efforts were being made to address the issue, he said.
Relentless hit-and-run raids, as well as suicide bomb attacks, were hard to deal with by conventional means, he argued.
“There is really what I would call battle fatigue,” he said, adding that retraining would help combat the jihadists’ tactics.
On Monday evening, fighters loyal to factional leader Abubakar Shekau attacked Sajeri village on the outskirts of the Borno state capital, Maiduguri, killing three people.
At the same time, militants aligned to the Islamic State group-backed Boko Haram faction attacked a military facility in Auno, some 23 kilometres (15 miles) from the city.
The increase in attacks has seen the appointment of five different commanders of the military operation against Boko Haram in the last two years.
But Buhari has refused to sack his military top brass, unlike his predecessor Goodluck Jonathan, who removed senior officers as the jihadists began taking over territory.
“I accept responsibility for that,” Buhari said in the interview, adding that he was “measuring the options very critically”.
But he said that such appointments were not to be taken lightly.
“My understanding of security is that when you have a case of emergency you have to be careful with the head of (the armed) services,” he said.
Many of the attacks on military installations have been blamed on or claimed by the self-styled Islamic State West Africa Province (ISWAP), headed by Abu Mus’ab Al-Barnawi.
The group broke away from Shekau in mid-2016 in opposition to his indiscriminate targeting of civilians in the conflict. It has instead vowed only to hit “hard” targets.
Security analysts have interpreted the surge in ISWAP attacks as a sign of renewed strength and organisation, with possible support from the jihadist networks in the wider Sahel region.
In late December, a naval base and another for troops from a regional force fighting the jihadists were overrun in the Baga area, on the shores of Lake Chad.
Referring to Monday’s clashes, Babakura Kolo, a member of the Civilian Joint Task Force militia, said soldiers and the CJTF in Auno were attacked by Al-Barnawi fighters.
“There was heavy fighting and the gunmen were repelled with the help of a fighter jet,” he told AFP.
“The insurgents had two days ago warned residents of (nearby) Jakana to vacate their homes by Wednesday because they were going to launch a major attack.”
Meanwhile, a community leader from Baga said 10,712 people had registered at camps for internally displaced people in the garrison town of Monguno and Maiduguri.
All had fled their homes as the military prepares a fight-back.
“More people are trooping in because they are scared to live under Boko Haram. At the moment they don’t hurt civilians. They are only after soldiers and the CJTF,” he added.
In December, the National Emergency Management Agency said it registered 2,040 IDPs who fled Kukawa, Kuros-Kauwa and Bunduram communities in northern Borno following attacks.