O’Brien, who signed his first professional deal with the League One side in June of last year, initially joined on loan at the beginning of December.
The young defender has gone on to make seven appearances in total for the Boro.
He scored a dramatic late equaliser on debut in a 2-2 draw away at Matlock Town, and has helped Bobby Grant’s side to fourth place in the Northern Premier League table.
Since his arrival, Radcliffe have lost just once in 11 matches in all competitions, winning six.
They are next in action on Tuesday night against Glossop North End in the semi-finals of the Manchester Senior Cup.
Photo credit: Radcliffe
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