Declan John "was playing through a painful injury and put off his surgery" last season to help St Mirren avoid relegation, manager Craig McLeish has revealed as the left-back was rewarded with an extra year on his contract.
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The 30-year-old Welshman, who initially joined on a short-term deal in November 2024, is now contracted to the Scottish Premiership club until summer 2028.
McLeish described it as "a fantastic piece of business" to extend his stay further.
"Declan is a really important player for us and I think he's one of the best full-backs in the league," he told St Mirren's website.
"He brings so much experience and leadership on and off the pitch and is a core part of our experienced group of players.
"He was playing through a painful injury and put off his surgery to try and help us over the line. I think that speaks volume of Declan as a character and I'm delighted to have him for the longer-term."
John played for Cardiff City, Barnsley, Chesterfield, Rangers, Swansea City, Sunderland, Bolton Wanderers and Salford City before moving to Paisley and making 62 appearances, scoring three times and contributing 11 assists.
He said he is "not far away" from a return to full fitness and added: "The club has shown really good faith in me over the last couple of seasons.
"I think I've done quite well over my time at the club and it's nice for the club to come forward and offer me the extension."