Nathan Sowter, the Australian-born, England-qualified legspinner, has joined Durham on loan for the rest of the T20 Blast and looks set to leave Middlesex permanently when his contract expires later this year.
Sowter, 29, is Middlesex's third-highest wicket-taker in T20 history but is yet to feature in a matchday squad this year. He has been actively seeking a loan move and looks set to make his Durham debut against Lancashire on Friday night after agreeing to join them until mid-July.
He is available to play in all formats, and is unlikely to feature for Middlesex again, not least because he was retained by Oval Invincibles for the Hundred and as such will not be available to play in the Royal London Cup in August.
Sowter took 15 Blast wickets last season with an economy rate of 7.50 but the emergence of two spinners through the Middlesex academy - legspinning allrounder Luke Hollman and left-arm spinner Thilan Walallawita - has left him surplus to requirements.
The club's management have also opted to use one of their two overseas spots for the Blast on a spinner - Mujeeb Ur Rahman is due to replace Chris Green imminently - meaning that Sowter has not been called upon even when they have fielded three spinners in the same side.
ESPNcricinfo understands that Sowter was told shortly before the start of the Blast that he was unlikely to feature in their plans for the tournament and he has been looking for a loan move over the last two weeks.
"Sowts hasn't been selected for any first-team action this year due to the progression of other players within the squad," Alan Coleman, Middlesex's head of performance, said.
"We have made a conscious decision to give match experience and opportunities to those players, with an eye on building our longer-term plans. Sowts is a great bloke and we wish him every success during his loan spell with Durham at the Riverside."
Scott Borthwick, Durham's legspinning allrounder, is unavailable for Friday night's game due to a wrist injury which requires an injection, so the club have signed Sowter as cover. If he impresses over the next few weeks, it could be the precursor to a permanent deal.
Middlesex started the season brightly, winning their opening three matches, but have now lost four games in a row, while Durham are eighth out of nine in the North Group after two wins and five losses from their first seven games.