"We were looking forward to having a great start to the [Champions League] campaign," Christensen told the club's website.
"We felt we were on top for most of the game. Valencia had some spells but we knew that was going to happen and we were ready for it. We kept working. Our work ethic was good all game and it felt we controlled most of it which is why it is tough to accept the goal against and the result in the end.
"We are not happy to let goals in from those situations and we know it can be costly, but now we look forward to the next game."