Brentford face the second-place Blues in on Sunday.
"They are maybe even more in-form than Liverpool, even though they are top of the league," said Frank.
"They are playing incredible football and are well-coached. Maresca has done a top job so far with his coaching staff and they look extremely dangerous.
"(Chelsea) have so many threats going forward and have top-quality players all over the pitch. I expect an unbelievably difficult game.
"They are massive favourites but, of course, we believe that we can compete against anyone and we believe we can win."
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