The Premier League side came in with a loan offer for the Colombian in the final hours of Froday's window which the Whites appear to have accepted but there is no guarantee a move will go through.
Although deals are supposed to be done by 11pm, clubs can apply for a "deal sheet" which gives them a two-hour extension. The Cherries may have to do this if they are to complete the move.
The transfer was one Daniel Farke had gone into the last hours of the window expecting to see off.
Earlier in th afternoon manager Farke had told the media that barring "a crazy offer" he expected the winger to stay at Elland Road for the rest of 2023. For what it was worth, Sinisterra apparently told supporters as much as he left Thorp Arch after a training session his manager said he worked well in.
Leeds' late August dilemma has revovled around Sinisterra and Willy Gnonto, both of whom made themselves unavailable to play in order to try and force moves.
Both appeared to have backed down and were reintegrated into the team at Ipswich Town, where each scored in a 4-3 win.
But the concern with Sinisterra was that his agent was still fighting a battle behind the scenes over the interpretation of his release clause, having seen a slew of team-mates leave on those technicalities. Leeds had to weigh up if keeping Sinisterra might prove to be more hassle than it was worth.
The answer from Farke early in the afternoon appeared to be that it was, but someone in the club seems to have decided otherwise.
Leeds had been linked with a move for Roma's Norwegian winger Ola Solbakken but the beyond-the-last-minute nature of this deal may make that impossible.