Mikel Arteta admits Arsenal face a 'really tough' Europa League semi-final against Villarreal.
The Spanish side are managed by former Arsenal boss Unai Emery, who has won the competition three times.
Asked about facing Villarreal, Arteta replied: "It will be really tough and Unai is probably the most successful manager in this competition."
The semi-final first-leg will be played on April 29.
The second leg will be played a week later on May 6.
On the performance against Slavia, Arteta added: "Well really happy. We came into a tough place this team hasn't lost at home in almost two years.
"I think when we demand them efficiency today is a good example of the efficiency you need in Europe to win matches."
