The possibility of Singh holding additional charge of Finance arises more particularly in the view of the difficult situation the economy was passing through.
Mukherjee will resign before he files nomination for the election after the return of the Prime Minister from his nine-day foreign trip on June 23, according to MoS in the PMO V Narayanasamy.
Singh had earlier kept the charge of Finance Ministry for a short span during the UPA-I when P Chidambaram was moved to Home in the wake of Mumbai terror strikes in November 2008.
Mukherjee's likely movement from North Block is also likely to lead to consequential changes in the Council of Ministers.
There are questions on the continuance of Trinamool Congress in the UPA in the wake of its revolt in the Presidential poll and its decision to field a candidate against the coalition's nominee.
Should Trinamool quit on its own or is shown the door, then ministries held by its members, including Railways at the Cabinet level, would become vacant needing replacement.
A reshuffle may also open possibilities for claims by parties like DMK to seek ministries it lost after the resignation of A Raja and Dayanidhi Maran.
Another important post that will become vacant is the Leader of the House in the Lok Sabha held by Mukherjee.
