Robert Abela said Labour Party delegates should not "turn back the clock" when asked about Jason Micallef's bid to run for the post of deputy leader for party affairs.
The prime minister's less-than-enthusiastic response to Micallef's candidacy came during an interview with LovinMalta, where he asked what he made of the VCA chairman's plans.
The interview was recorded on Thursday, a day before Micallef confirmed that he intended to run for the position, which delegates are expected to vote on at the party's next general conference in September.
"Jason Micallef gave his contribution in the past and I feel he still has a lot to give. If this rumour is true, then it is up to the party delegates to pass judgement," Abela said.
He said party delegates have always passed good judgement to keep the PL a "winning movement", he said, adding that the party's goal in selecting its leadership is not only to win elections but to keep the organisation in the best state possible to keep doing good in the country.
He urged delegates to ensure that the party continues to open itself up in a way that is more appealing to moderate voters and in general to become more accessible to a wider band of voters.
"Every time in the past that the Labour Party closed itself up, it lost the election. This is clear," Abela said.
"It lost every time it encapsulated itself and adopted a siege mentality. So I want to appeal to the middle ground."
When asked whether Micallef appealed to the middle ground, Abela replied that it was up to the delegates to decide.
"What I can say is the same reply I gave you earlier, you cannot turn back the clock, you can only go forward," Abela said to quantify his response.
"You asked me about a specific person, but I think my reply counts in general, when your time is up and you've given your contribution, don't come back."
Micallef served as general secretary of the Labour Party between 2003 and 2008 when Alfred Sant served as leader. He was re-elected soon after Joseph Muscat became leader in 2008 but the post was abolished a year later to make way for the unelected post of CEO.
Micallef is known as a staunch supporter of Muscat.