Buckley is set to join Leeds on a 93-day emergency loan next week, a deal which secures one of Rosler’s long-term transfer targets and will keep the winger at United until the start of the January window.
Terms with Sunderland are agreed and Buckley is already training with Rosler’s squad but his transfer has been delayed to ensure that his loan does not expire in the middle of the Christmas schedule.
Football League rules limit emergency loans to a maximum of 93 days and the timing of Buckley’s arrival will keep him at Elland Road until January 2.
Leeds will then have the option of re-signing Buckley on a permanent basis or on a half-season loan to the end of the Championship term.
The winger is in line to make his Leeds debut at home to Birmingham City next weekend having been ruled out of the clash with Boro.
Rosler said: “We needed to use common sense.
“To have Will throughout the whole Christmas programme is far more beneficial than for the Middlesbrough game. Not only thinking short term, we needed to see the bigger picture as well.
“Our aim is also to give the player a clear incentive; to say ‘listen, we want you for 93 days but we want you at least for the whole season.’ It’s better for the player too in terms of him not having to go back for 10 days to his club where he’s clearly not (wanted).
“It’s better to keep him close and then hopefully we can get an agreement with Sunderland and the player that he carries on for the whole season. Hopefully we’ll get a permanent (deal). That’s what we always try to do when we loan a player.”
Buckley - Sunderland’s £2.5m signing from Brighton last summer - has been frozen out at the Stadium of Light and was targeted by Leeds repeatedly during the summer.
Attempts to recruit him on a long-term basis were thwarted by the player’s wage, understood to be in excess of £20,000 a week.
United signed two other wingers - Stuart Dallas from Brentford and Jordan Botaka from Dutch club Excelsior - before the summer window closed but a lack of depth has seen Sam Byram feature regularly on the right side of midfield.
Rosler said: “We worked for a while on Will. Finally we got him
“It was no secret that we tried to improve in wide areas. There was a lack of natural wide players in the squad. Sam Byram has had to help out.
“Will knows the Championship well. He’s a proven Championship player with proven quality. He can go right into our team and make us better.
“We’re very happy that we’ve got him on loan with a view to be here throughout the whole season. That’s our target and Will’s target too.
“He’s fearless running up the pitch. You don’t need to combine to get 50, 60 yards up the pitch. Will can take the ball and carry the whole team. He’s got energy, experience, he’s a good age and he’s got a point to prove after his time at Sunderland.”