Flint, who was shadow energy secretary under Ed Miliband, will probably not declare until the timetable for the process is set out after a national executive committee meeting on Tuesday. However, sources close to the Yorkshire MP said she was almost certain to throw her hat into the ring.
Watson is the only candidate for deputy at the moment and launched a crowdfunding attempt on Sunday to raise £25,000 for his bid.
The race to be deputy looks set to be an even starker clash between the Brownites and Blairites within the party than the race for the leadership. Watson, who campaigned against phone hacking, is deeply involved in the trade union movement and the old Labour wing of the party.
In contrast, Flint’s politics are closer to those of Blairites Chuka Umunna and Liz Kendall than those of the other potential leadership candidates Yvette Cooper and Andy Burnham.
Gloria De Piero, Miliband’s shadow equalities minister and a former GMTV presenter, is also a strong contender to be deputy leader, possibly on a ticket with Tristram Hunt as leader.
Another possible choice for the deputy leadership is Angela Eagle, who was shadow leader of the House of Commons and delivered impressive performances in parliament against her Tory adversary, William Hague.
The slate of potential deputies will be crucial to those running for leader as they seek to shape the future of the party in the aftermath of a crushing defeat at the hands of David Cameron.
There may be some pressure in the Labour party to choose a woman as the next leader, but having strong female deputy leadership candidates could address this.
Flint was often sent out to promote Labour’s campaign in the media, especially after the television debates, and trebled her majority in Don Valley at the election.
It is understood she feels Labour needs to win back working- and middle-class voters in the south of England but wants the party to take time to reflect on what went wrong.
This article was written by Rowena Mason Political correspondent, for theguardian.com on Sunday 10th May 2015 14.02 Europe/Londonguardian.co.uk © Guardian News and Media Limited 2010