Gera raptured his anterior cruciate ligament against Tottenham on Saturday and will miss the rest of the season.
Foster has both been out with similar injuries.
He said: “It’s a big blow for Zoltan. I could see from where I was that it was going to be a bad one.
“He seemed to twist badly and I feared the worst straight away. Sadly it looks like it is.
“I know what he is going through having suffered a cruciate ligament injury twice myself – at Stoke and then Manchester United.
“It’s horrible but both times I’ve come back strongly. Zoltan will come back from this and be a better player for it.
“He’s got the right attitude and mentality.”
