"The matter is proceeding tomorrow (Monday)," his spokesman, William Bango told AFP.
The court sat for one day last month, after a four-month break in the high-profile trial of the leader of the official opposition, the Movement for Democratic Change (MDC).
The 2 December hearing was brief because state lawyers had lodged an application with the court to tighten the charges against Tsvangirai.
Bango said the MDC expected Judge Paddington Garwe to deliver his ruling on Monday before the trial proceeds.
"We are expecting a ruling on whether they (the state) can alter the charges or not," Bango said.
Tsvangirai is on trial for allegedly plotting to assassinate Mugabe and arrange a military coup before the March 2002 presidential election, which he lost to Mugabe.
He denies the charges for which he could be hanged.
The state accuse Tsvangirai, who attended a meeting in Montreal, Canada in December 2001 with political consultant Ari Ben Menashe, of allegedly requesting help to eliminate Mugabe ahead of 2002 presidential elections.
A grainy and partially audible black and white videotape has been produced in court as evidence of that meeting.
But in December, 11 months after the start of the trial, state prosecutors sought to amend the charges to include "discussion on transitional arrangements after the assassination (of Mugabe) as well as seeking military support after the elimination".
Mugabe was the target of the
alleged assassination plans
Defence lawyers opposed the application, arguing the changes were equal to laying fresh charges against Tsvangirai.
Tsvangirai faced the initial treason charges along with his party's Secretary General Welshman Ncube and shadow agriculture minister, Renson Gasela. But charges against the two were later dropped.
If the judge rules in favour of the state on Monday, Tsvangirai will be called to the witness stand for the first time since the trial opened in February last year.
But procedurally, Ncube and Gasela will give evidence before Tsvangirai.