Robert Abela is "concerned" that tensions may boil over when Labour supporters gather to support Joseph Muscat outside court on Tuesday.
"I am concerned because I have the interests of our country at heart. I am concerned there might be tensions that this country does not deserve. I am concerned that a Maltese citizen might do something that hurts another Maltese citizen," the Prime Minister said as he fielded journalists' questions at the end of an event.
Abela's comments come as his predecessor is set to face charges for a raft of financial crimes related to the brokering of a deal that saw three state hospitals privatised.
Following the conclusion of an inquiry, he is set to face money laundering, corruption and bribery charges, among other serious accusations.
Muscat's allies are organising a "solidarity meeting" in support of the former prime minister in front of the law courts around the same time as the arraignment.
Muscat's staunchest supporter, broadcaster Emmanuel Cuschieri, announced the solidarity meeting earlier this week. Valletta Cultural Agency chair Jason Micallef, as well as Muscat's lawyer and former PL MEP candidate Charlon Gouder, have also voiced support for the event.
In a post to a Labour supporters Facebook group, Muscat's wife Michelle thanked Cuschieri for his support and for not leaving anyone "alone in the moment of truth".
But Muscat himself has tried to cool down enthusiasm for the meeting, urging supporters to instead use their vote for the Labour Party as a show of confidence in Muscat.
Speaking to journalists on Thursday, Abela said: "There is a sacred right to show solidarity, and there are several ways to do that, but I also have the obligation to appeal for everyone to act responsibly".
No one should succumb to provocation, and "absolute calm" should be maintained.
"We should not risk losing the spirit of national unity that has forged this country over the years in a minute," Abela said.
Abela spoke with a more conciliatory tone on Thursday when compared to statements he made earlier this week.
On Tuesday, Abela alleged that the Nationalist Party is setting a "trap" for Labour supporters who attend the gathering by stoking tensions.
The prime minister again talked of a "trap" on Thursday and said: "No one should fall into a trap. But naturally, if anyone falls into a trap, there will be repercussions for who set the trap but also for who fell into it".
Muscat himself has attempted to cool down the fervour surrounding the "solidarity meeting".
On Tuesday, Muscat said that voting for the Labour Party in the upcoming June 8 elections was the best way to show solidarity with him.
He further dissuaded the gathered crowd from attending the Tuesday demonstration by saying, "The greatest solidarity you can show with me, my friends, is not to take leave from work to come to Valletta."
Abela said he agreed with Muscat's comments.
The prime minister also distanced the Labour Party from the planned event, which is expected to draw a strong police presence.
"None of my people are organising anything; it is absolutely not organised by the Labour Party."
It is the first time that a Maltese prime minister is facing criminal charges in court.