The manager described Tosun's situation as a "massive, and cruel, blow", expressing huge sympathy for the Turkish forward who had settled in well in South London.
He said: "It’s a real blow, it’s a massive blow in particular for him. He was starting to really find his feet at the club, and was hoping to play a much bigger part than he’s had in the last couple of years at Everton.
"He was looking good in training – we were really thinking it’s going to be great having him with us for the latter part of the season – because he would have brought something we don’t necessarily have within our squad.
"For him to get this really bad knee injury, it’s come at a really bad time for everybody – most importantly of all for Cenk. He takes his international football very seriously – he wants to play for his country, so to be hit by this cruel blow, it’s very difficult for him – and we have enormous sympathy for him here at the club – and we really do wish him well with the surgery and hope to see him back very soon. It’s a massive blow to us and to the player."
Whilst the Tosun news "hit us for six", elsewhere it was a very positive picture painted by the boss. He said: "James Tomkins has recovered and trained with us this morning [albeit] in a lighter way, but he’ll be back in full training on Monday."
The manager also confirmed that Jeffrey Schlupp and Mamadou Sakho were back in full training with the squad this week, and suggested that all are "fit and raring to go".
Watch Roy's full press conference on Palace TV now.