The leader, who declined to be identified, said it would be ideal if Sonia becomes the Leader of the Lok Sabha and there may be a deputy also.
The leader recalled that Sonia was the Leader of Opposition in Lok Sabha before Congress came to power in 2004.
He insisted that it was only a convention and not a rule for the Leader of House has to be a Cabinet Minister.
Only last week, 10 party MPs had favoured Rahul Gandhi to take up the post, which has fallen vacant after Pranab Mukherjee was elected President of the country.
DMK has already urged Sonia to become the Leader of the Lok Sabha.