UPDATE 1-TNK-BP head of upstream to leave company-sources

* Highest ranking exec to leave since shareholders fell out

* BP may sell TNK-BP stake to Rosneft, AAR may stay or sell

* Dodds unlikely to join colleagues at Rosneft

* Deputy seen as likely successsor

(Adds background on Dodds, likely sale of shareholders' stakes in TNK-BP)

MOSCOW, Oct 11 (Reuters) - The head of upstream at Russian oil firm TNK-BP will leave the company, the highest-ranking executive to depart in an exodus of staff as a potential sell-off by its main shareholders looms, sources close to TNK-BP said on Thursday.

Alexander Dodds joined TNK-BP from ExxonMobil Qatar , where he had served as president, in October 2011. The sources said his resignation would be announced to company staff on Friday.

Senior TNK-BP staff, including its top oil trader and head of mergers and acquisitions, have left the company in the months since BP and its partners in the Russian-British oil company said their 50-50 joint venture was untenable.

Both sides have said they are willing to sell out, though the quartet of Soviet-born billionaires who share control of the No.3 Russian oil producer have also said they would be willing to buy out the British oil major.

Russian state-backed oil firm Rosneft has said it would like to buy out BP and is seeking financing for the deal, likely to be worth a total of $25 billion or more, though a full merger of TNK-BP and Rosneft through a buyout of both partners could be difficult to finance.

Dodds is seen as unlikely to join a steady flow of executives from TNK-BP and BP itself to Rosneft, however. Sources close to TNK-BP said his likely successor was his deputy, Nikolai Ivanov.

(Reporting by Melissa Akin and Vladimir Soldatkin; Editing by Megan Davies and Mark Potter)

((melissa.akin@thomsonreuters.com)(+7 495 775 1242)(Reuters Messaging: melissa.akin.thomsonreuters.com@reuters.com))