The versatile centre-back joined the Welsh club last month during time back home for ‘personal reasons’.
The Wales under-21 international scored twice in eight appearances with the Martyrs and was expected to be with them until January 4.
But with Reds defender Joe McNerney currently sidelined and Mark Connolly spending time in an intensive care unit at hospital after receiving a blow to the windpipe in Saturday’s crushing 3-1 defeat to Cambridge United, head coach Dermot Drummy has been forced to act.
Alex Davey started but struggled through the League Two clash at centre-half two days ago, while Addison Garnett, who came on for his League debut, and had a more assured display is only just back from injury.
With Connolly a doubt for tomorrow night’s FA Cup replay at Bristol Rovers, Yorwerth’s recall helps cover dwindling numbers in the backline.
Merthyr boss Gavin Williams said: “Obviously we are gutted to be losing Josh, he has been fantastic for us during his time here. But he is a Crawley player, and they need him back.”
“I would like to thank Josh for his commitment during his time here, and wish him well back at Crawley.”
Yorwerth joined Reds on a one-year deal in the summer following a successful loan period from Ipswich with the League Two club the previous season.
The former Cardiff City man has made six appearances for Reds this season, the last against Portsmouth.
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