Athletic Bilbao striker Fernando Llorente has singled out Wayne Rooney as Manchester United's main threat ahead of their Europa League last-16 tie.
The Spanish side travel to Old Trafford for the first leg of the clash on Thursday, their first trip to the stadium since 1957.
Bilbao finished sixth in the Primera Liga last season, 38 points behind winners Barcelona, and knows they go into the tie as huge underdogs.
"Manchester are obviously the favourites. They always play Champions League and compete with teams like Barcelona and Real Madrid," Llorente told the Europa Press Association.
"They are one of the big teams in Europe and we're novices.
"Rooney is a real killer. He has a great mentality and is a great inspiration for his team-mates.
"I expect a very exciting game. We are really looking forward to the game, and will do our utmost to get a good result. We have been doing quite well and might cause an upset."