Stoke City boss Tony Pulis admits they're not in the class of tonight's opponents Arsenal.
Pulis was impressed by Arsenal in their victory over Barcelona last week.
"I went to their game with Barcelona, and it was a fantastic game," said Pulis.
"For all of Barcelona's dominance, and they were very dominant at times, Arsenal still had very good chances. Robin van Persie could have scored a hat-trick.
"Arsenal will be delighted to be 2-1 ahead and heading out for the return with a great opportunity of going through. It means the second game will be a great one.
"But in watching that game I can say we're not on their level, I think everybody accepts that.
"So we just have to go there and do our best, and that's what we'll do.
"We have to be switched on. It's a game we know will be very, very difficult, even if we play at our best. If we don't, then we're in trouble."
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