Aberdeen defender Tommie Hoban has been ruled out for the remainder of the season with the second cruciate ligament injury of his career.
Hoban, 25, is on a season-long loan from Watford and missed the 2017-18 campaign with damage to his other knee.
He went off injured shortly during Saturday's 2-2 Scottish Premiership draw at home against St Mirren.
"We are liaising with Watford FC to plan the next steps ahead of his operation," an Aberdeen statement read.
Hoban has made only nine appearances since joining Aberdeen in July.
He scored his first and only goal in a 1-1 draw with Hibs in August, but he was sidelined thereafter with a shoulder injury until his return as a substitute in the 0-0 draw with Kilmarnock last month.
And Hoban said on Twitter: "Struggling to come to terms with what happened at the weekend and really can't believe I'm in this position again."