David Miliband could be in line for a senior post envisaged under the impending Lisbon treaty.
The foreign secretary is the focus of speculation over the high representative role, an effective foreign minister for Europe, which would be created if the treaty comes into force.
His candidacy could only be realistic if Tony Blair does not assume the European Commission presidency. The former prime minister is a hot favourite for the senior role but his close association with the Iraq war, which many EU members opposed, could derail a potential bid.
If Luxembourg's Jean-Claude Juncker or another rival gets the presidency many diplomats are indicating Mr Miliband, who could be on the backbenches within six months if Labour lose the coming general election, may be a viable alternative.
"People are going to talk positively about Miliband," a European diplomat told the Guardian newspaper.
Another told the Times: "He is effective and well liked. He has an ability to combine tactics with an understanding of the political big picture and people find that very impressive."
Mr Miliband's credentials could receive a huge boost if a major speech to the International Institute of Strategic Studies on Monday goes well.
The foreign secretary will discuss the EU's role as a global actor and the benefits for the UK of a strong EU foreign policy.