Northampton Town defender Rod McDonald has signed a contract to keep him with the club until the summer of 2018.
The 23-year-old former Hereford and Telford centre-back joined the Cobblers in the summer and has made 20 appearances for the League Two leaders.
He has helped them to four successive clean sheets in recent matches and a club-record nine straight league wins.
"Rod has made terrific progress this season and we are delighted to tie him down," said manager Chris Wilder.
"We have worked hard with Rod, he has learnt a lot and while he still has more to learn, there aren't too many young, left-footed central defenders around.
"We are delighted to have secured the future of a very promising and talented young player."