Okore has been ruled out for the rest of the season after suffering a cruciate knee ligament injury in just his fourth game for the Premier League club.
"Jores is so unlucky with his injury," Vlaar told the club's official website. "He's going to come back very strong. A lot of it is mentally, and that's where we have to help him, because sometimes it will be difficult.
"I think he did really great in the games he played. I know what he's going through and I hope that if we can have good results it will help him feel better.
"We try to help him as much as we can. He has to go on. It's going to be a long way but he's going to come back stronger.
"I will talk to him, I talked to Gary Gardner last year. It's little things, you have to try to give yourself a good feeling.
"Make yourself happy even if it's hard, because it's a way of helping yourself recover on your own.
"You do have to do things on your own but we'll try to help him as much as we can."
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