French Conservative Senator Jean Bizet claimed Macron had to step-up but warned the new unofficial role would be “very difficult” for Mr Macron.
Mrs Merkel’s decision to quit politics after her current term as Chancellor ends in 2021 sent shockwaves across Europe and the world yesterday.
Sen Bizet said: “Germany has been the strongman of Europe for many years but today it has become the weak man, if I may say so.
“Everything rests – and will rest more and more – on president Macron’s shoulders. It will be very difficult for him.”
Emmanuel Macron is poised to take over from Angela Merkel as the leader of Europe
Mr Bizet, the chairman of the senate’s committee for European affairs, told the TV channel Public Sénat the German leader’s decision to not seek a fifth term as chancellor was “a great disappointment but sadly an expected disappointment.”
He added: “It’s bad news for the coalition, bad news for Germany, bad news for France but also bad news for Europe”.
Mrs Merkel, 64, announced her decision to retire in 2021 and also step down as leader of the Christian Democrats (CDU) after her party on Sunday suffered its second regional election setback in as many weeks.
The CDU and its Social Democrat coalition partners suffered heavy losses in the weekend’s regional election in the large central state of Hesse, home to the financial capital Frankfurt.
But stepping down as CDU chairman further undermines Mrs Merkel’s authority, as she had previously said the party chair and chancellery should be held by the same person.
While Mrs Merkel has dominated European politics since 2005, helping guide the Brussels bloc through the eurozone crisis, her decision in 2015 to open Germany’s doors to more than one million migrants fleeing war in the Middle East caused deep divisions within the EU and weakened her support.
Mr Bizet said: “Big European issues cannot be solved alone. But in this case, Angela Merkel did not consult with her European partners before making a unilateral decision that completely upset the European Union’s social balance.”
He added that mass immigration “weakens the single market”.
But while Mr Macron is thought to be plotting for France to take over from Germany as Europe’s engine, he was effusive in his praise of Mrs Merkel when commenting on her looming retirement later on Monday.
The 40-year-old centrist hailed his allies “very respectable” and “dignified” decision to not run again after the end of her term, as he paid tribute to her ability to face financial and migrant crises in recent years without forgetting Europe’s fundamental values.
“She leads her country with much courage,” he told a news conference in Paris.