The four-time England international moves to the County Ground for the concluding weeks of the domestic summer, having agreed a three-year deal with Mickey Arthur's side in July
Derbyshire have fast-tracked the arrival of Pat Brown after acquiring the Worcestershire seamer on loan ahead of his permanent move to the County Ground.
It essentially brings an early end to the England international's career at New Road, which began at the age of 17.
Mickey Arthur has a depleted bowling attack ahead of the final three County Championship matches of the season, with Suranga Lakmal having not played since mid-August and Ben Aitchison out with a lower back injury.
They travel to Gloucestershire in the next round from Sunday (September 10) before hosting Sussex (from September 19) and taking a trip to south Wales to take on Glamorgan (September 26).
Brown was not involved in Worcestershire's Championship win over Glamorgan - he hasn't played a first-class match since 2018 - and will have no part in the club's Division Two promotion push.
Brown's Worcestershire white-ball form saw him capped by England in New Zealand in 2019 (Gareth Copley/Getty Images)
In 91 matches across formats, Brown took 123 wickets - 48 in T20os across 2018 and 2019 as the Rapids first won the Blast and then reached the final the following year.
That streak saw him recognised by England, playing four T20Is during the New Zealand tour in 2019.
But attempts to build on that breakthrough have been affected by a string of back injuries.
"We needed some cover for our bowling attack and this gives us a chance to see Pat in action and get a look at what he can bring to our group," explained Arthur.
"He's an experienced bowler and someone who has played at the highest level, so we're looking forward to seeing what Pat can do for us this month."
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