Hearts boss Craig Levein confirmed the 32-year-old would be sidelined for “six to eight weeks”, adding that the on-loan forward may need an operation after a scan showed damage.
Naismith was forced off less than ten minutes into the 3-0 defeat at BT Murrayfield with a knee injury, and joins club captain Christophe Berra, Uche Ikpeazu and John Souttar on the sidelines.
Levein said this morning that there appeared to be a “slight tear in the knee cartilage,” which would require surgery and a period of recuperation, adding that Naismith had returned to parent club Norwich City for assessment.
“It looks like he’s got a little tear in his cartilage, which we suspected,” Levein said. “[He’ll be out for] maybe six to eight weeks or something like that - but I’m guessing.”
Naismith has captained Hearts in recent matches following the injuries to Berra and Souttar, and has been integral to Hearts’ stay at the top of the Scottish Premiership, with 11 goals in 16 games for the league leaders.
He will now miss a string of matches for the Jambos, starting with Wednesday’s derby with Hibs and Saturday’s trip to face Celtic.
Levein added: “We’ve had a number of blows in the last three or four weeks so we will just have to cope with this one as well as we have done with the other ones.
“It does leave us a bit thin on the ground up top with Uche [Ikpeazu] being out as well, but we’ll get by.”
Naismith will almost certainly miss Scotland’s key UEFA Nations League matches against Albania and Israel later this month, in a further blow to Alex McLeish.
The former Everton and Rangers man scored in the first match against Albania and grabbed a consolation in the 3-1 friendly defeat to Portugal.