The Reds manager leveled blame for the injury at Tottenham defender Micky van de Ven, describing the tackle on Isak as reckless.
"I'm obviously disagreeing in many ways," said Spurs boss Frank in response. "We are talking about a defender in Micky van de Ven that will do everything he can to avoid the goal.
"So it's a transition. So he's sprinting back in. There's a ball slid down the side and he does everything he can to see if he can block that shot. So he's sliding.
"Unfortunately, Isak plants his foot straight there and that makes it look worse than it is. I think that would be a natural reaction for any defender.
"I'll put it this way, if my defenders don't do that, then I don't think they are true defenders. So I don't see that at all.
"Normally, you haven't seen any reckless challenges from Micky. As I remember it, he's a very fair and competitive player.
"So that's one thing. The other thing, you also know that the two players have sorted it out. They have spoken. So that's a good sign of how they sorted it out. A good sign."