The French defender suffered a fractured fibula on Wednesday night, the 20-year-old taken to hospital after he was stretchered off during the club's 3-2 win over Villarreal.
“It's never nice to see when people get injured, especially your team-mates," Bertrand said.
“It took the whole mood of the game. It was tough, especially with the changes, finishing the game from that moment. It killed the whole momentum that we had built up in that moment.
“(The mood in the dressing room is) down, just frustration I think. It's never nice to see, in an opponent, your team-mate, your friend. It's someone who has a big part to play in this team.
“He's an unbelievable player. I've been fortunate to play with some decent centre-backs in my time, our centre-backs are both right up there.
“Wes, at such a young age, has shown fantastic promise. It's so unfortunate, but we're all around him. I'm sure he'll come back stronger and we will be there supporting him."
He added: “That's a bit more of the gutting thing, tonight we've been working on shapes and our connectivity and our fluidity within the back-four unit.
“You might have seen me dropping in as a three, with Ricky going higher and then me arriving late on the other side when we're attacking.
“We've been working on it and tonight we had that togetherness within us, we had good balance, good possession, we had that rhythm."
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