Hibernian: Jason Naismith and Ryan Porteous surgery confirmed
Hibernian say Jason Naismith will be sidelined for six months while fellow defender Ryan Porteous has also suffered a serious knee injury.
Porteous, who has also been handed an improved contract, "is optimistic of appearing before the end of the campaign", the club report.
It is the second January in a row that Porteous has picked up a knee injury that required surgery.
Naismith is on a season-long loan from Peterborough United.
The 25-year-old also missed much of 2015-16 season with a knee injury while with St Mirren but has played 14 games for Hibs after being signed as a replacement at right-back during the injury absence of captain David Gray.
Gray made his own first appearance since August as he took over from Naismith at half-time during the 2-2 Scottish Cup draw against Dundee United in which the latter and Porteous were injured.
Centre-half Porteous, who did not return to action until August, has gone on to play 16 times this season for the side sitting sixth in the Scottish Premiership.
Sporting director Graeme Mathie said of the 20-year-old: "We are delighted to reach agreement with Ryan and his representatives to improve the terms of his contract.
"Ryan has worked his way to a point that he's considered a key first-team player and we were delighted that he will continue his progression at the club for the foreseeable future."
Hibs were denied a place in the last 16 of the cup after goals from Lawrence Shankland and Louis Appere cancelled out Christian Doige and Martin Boyle strikes, with the two meeting again in Edinburgh on 28 January.