Andy Carroll is on the brink of joining West Ham permanently after passing a medical with the Premier League club.
Brighton have threatened to take action against the LMA as the dispute with Gus Poyet rumbles on.
The former England Under-19 international will spend an initial month with the Minstermen.
The 23-year-old right-back, yet to make his senior debut for Swansea, was signed from Welsh rivals Wrexham last year for £200,000.
Obeng becomes York's fifth recent signing following the arrivals of striker David McDaid from League Of Ireland Premier Division side Derry, teenager Jack O'Connell, on loan from Blackburn, fellow defender Jameel Ible, 19, from Salford City and striker Ben Everson from Icelandic side Breidablik.