Gul said the premier, who is on an official visit to Pakistan, is expected to announce the reshuffle after he returns late today.
"We have held long talks with the prime minister on ministers... He is making preparations and evaluations. We will meet when he is back and you will get an answer following this meeting," Gul told reporters in Ankara.
Erdogan, who was already expected to change up his cabinet ahead of local elections on March 30, is expected to replace 10 ministers - almost half the cabinet, according to media reports.
Twenty-four people including the sons of Interior Minister Muammer Guler and Economy Minister Zafer Caglayan, as well as the chief executive of state-owned Halkbank, have so far been charged as part of three separate investigations into the bribery allegations.
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Erdogan, who has led Turkey since 2002 as the head of a conservative Islamic-leaning government, has described the probe as "a smear campaign" to undermine Turkey's ambitions to become a major political and economic power.
The premier has responded to the probe by sacking dozens of police chiefs.
In his first direct response to the graft controversy, Gul said allegations of bribery can not be covered up.
"The judiciary is independent. If there is corruption, it can't be concealed. Everyone should be respectful of the judicial process. The judiciary will reach the right conclusion," he said.
Observers say the wide-ranging investigation has exposed a rift between Erdogan's Justice and Development Party (AKP) government and Fethullah Gulen, a hugely influential Muslim cleric who lives in the United States.
The Gulen movement wields considerable influence in Turkey's police and in the judiciary.