"I won't be part of the new government", Gabriel said on Twitter, adding that the German Social Democratic Party (SPD) parliamentary group head Andrea Nahles and SPD interim leader Olaf Scholz told him about this fact.
Maas has no particular diplomatic experience but has earned a solid reputation in the past four years as justice and consumer affairs minister.
If confirmed, Maas would replace another SPD politician, Sigmar Gabriel, in the role.
The post of top diplomat is crucial as the Nazi era and World War Two recede into history and Germany gradually takes on a more assertive worldwide role to match its economic might.
Germany's Justice Minister Heiko Maas will take over as foreign minister in Chancellor Angela Merkel's next government, media reported Thursday.
Mamata Banerjee declares support for Congress candidate for Rajya Sabha
At the regional level, Mamata's support for Singhvi is certain to drive a wedge between the state units of the Congress and the CPM .
However, most commentators expect Merkel to keep a grip on ties with the United States, Russia, China and the European Union as it negotiates Brexit and euro zone reform.
Merkel's conservatives and the SPD have agreed that the party will retain control of the foreign ministry in their "grand coalition" and the party is due to officially announce its six cabinet ministers on Friday.
Mr Gabriel is said to have a broken relationship with Mr Scholz and Ms Nahles. Katarina Barley, 49, family minister since 2017 who is a passionate pro-European with a British father, and Thomas Oppermann, 63, current vice president of the Bundestag, are also in the running. Barbara Hendricks, SPD environment minister in the outgoing coalition, has said she will leave office.
Merkel's next cabinet will include five more SPD ministers under a coalition deal that ended six months of political stalemate following inconclusive elections last September 24.
Merkel drew much criticism from within her Christian Democrats for handing the SPD the finance portfolio, traditionally the preserve of her conservatives.