The Magpies' number one has been ruled out for the rest of the season.
The Dutchman is out for the rest of the season with a ruptured ACL sustained while on international duty with Holland and McClaren lamented the recent turn of events.
"It's a bitter blow for Tim and for us," said the Newcastle manager.
"I spoke to him on the morning of the game, he wasn't playing and - selfishly - I thought that was good, because then he would be fit for us. Then I got the news, the severity of the injury and how he did it, and it's a massive blow.
"Tim is a big part of us - he's a big player, a leader in the dressing room, and his goal was to establish himself in the Dutch side going forward.
"We will miss him for the rest of the season, and he loses seven or eight months of his career,” he added.
Krul’s absence has left the Magpies with a crisis between the sticks, with second choice stopper Karl Darlow also currently out injured.
Responsibility has now fallen to third-in-line Rob Elliot and the 29-year old finds himself thrust onto the mainstage despite having not featured for the senior team since December last year.
The Magpies have had woeful luck with injuries this term - with the likes of Paul Dummet, Massadio Haidara and Cheick Tiote all out at various points – and McClaren will need his back-up keeper to quickly settle into his new role if they are to turnaround their season.
Newcastle are currently rooted to the table after a dismal start to the campaign but will take hope from the fact that their next few fixtures are a lot more winnable than the majority of their first eight – at least on paper.