Paul Lambert's men had not lost during November and carried on their fine form with a superb 3-2 victory against Southampton on Wednesday, before stumbling at Craven Cottage.
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"We were very disappointed in that result,” Clark told the club's official website. "After the midweek game - the win over Southampton - we were obviously looking to pick up another three points. It wasn't to be.
"When you go two-down just before half-time, it's a bit of a blow. But we wanted to come out, create some chances and nick the next goal. It would have turned in our favour and put pressure on them. But that wasn't to be.
"We didn't really create that many scoring opportunities which was frustrating. We had few chances. But if one had gone in it might have been a different story.
"We had a penalty appeal with five to go which should have been given. It was a disappointing afternoon.
"We were on a high. We have had a few good results. We were unbeaten in five. But we won't let this get us down too much.
"It was one of those frustrating games where we couldn't break them down. They put a lot of men behind the ball and did frustrate us. But we will move forward and now focus on the next game. We will go again at the weekend."