This means that Maroš Šefčovič, Slovak commissioner-designate for transport and space, would get the vice-presidential post for the energy union.

However, Bulc would only get transport, while it is not yet know who would get space.

Such a reshuffle would mean two hearings before relevant committees in the European Parliament would be needed, the same sources said.

Bulc would be heard on Monday, according to national broadcaster Radio Slovenija.

Juncker will officially announce his decision on the portfolio for Bulc and the other changes in his line-up today.

The post of the Commission vice-president in charge of the energy union had previously been allocated to Slovenia's first commissioner nominee Alenka Bratušek.

Bratušek however resigned after a poor confirmation hearing last week, so the Slovenian government put forward a new candidate.