Musharraf is not expected to be charged with murder, but over his alleged failure to provide adequate security for Bhutto, the lawyer Ahmed Raza Kasuri said Tuesday.
Bhutto, Pakistan's first female prime minister, was assassinated in a gun-suicide attack in December 2007, shortly after she came back to Pakistan from self-imposed exile to take part in the 2008 general elections.
Musharraf was president at the time.
A long investigation
Investigators said former Pakistani Taliban leader Baitullah Mehsud plotted the assassination and paid the equivalent of about $4,500 to a network of Islamist militants to carry out the killing.
But they also accuse Musharraf of failing to protect Bhutto. They say Musharraf rejected Bhutto's request to use a western private security contractor for protection when she returned to Pakistan.
They suggested Musharraf intentionally left Bhutto vulnerable because he felt politically threatened by her return.
The former military ruler has denied having anything to do with Bhutto's killing.
Musharraf's lawyer said the charges expected next week are politically motivated and that Musharraf plans to plead not guilty.
An investigation into Bhutto's killing has lasted nearly six years.
In May, gunmen killed a leading prosecutor working on the case, Chaudhry Zulfiqar Ali.
Reversal of fortune
Musharraf appeared Tuesday before an anti-terrorism court in Rawalpindi that's hearing the case, Kasuri said. The former military ruler is due to return to the court on August 6, when he is expected to be indicted, he said.
After the general elections in 2008 where his party was trounced, Musharraf stepped down as the governing coalition began taking steps to impeach him.
He himself then went into self-imposed exile.
Earlier this year, he returned to Pakistan in an attempt to revive his political career. It didn't work.
Instead, he's become entangled in a thicket of court cases related to his time as the country's top leader.
He has been under house arrest since April.
Musharraf did receive one piece of good news Tuesday when the court in Rawalpindi agreed to unfreeze his assets in Pakistan and abroad.
CNN's Saima Mohsin reported from Islamabad; Jethro Mullen wrote from Hong Kong. Shaista Aziz also contributed to this report.