Sevilla midfielder Piotr Trochowski is frustrated over his lack of progress.

The 28-year-old suffered a knee injury during the Spanish club's 3-2 home defeat against Barcelona in La Liga earlier this month.

Trochowski was substituted before half-time and was hoping that he would not need surgery.

However, a visit to Denver in the United States has confirmed that the German will have to go under the knife to repair the cartilage damage.

"I am not happy because I did not expect the injury to be so bad," he told Sevilla TV.

"Tomorrow, though, I am sure that I will feel better.

"Things were not improving and in the end we decided this had to be done and now I know that it is worse than first thought.

"I cannot say how long I will be out for. We will have to speak to the specialist and wait until after the operation to know more."