Sunderland new boy Jan Kirchhoff admits he is struggling with his fitness as he bids to adjust to the intensity of the Premier League.
Speaking to the Shields Gazette, the former Bayern Munich man said he has work to do if he is to improve.
He said: "To be honest, it’s a problem for me in the last 20 minutes.There’s days for me where there’s no issue and I can stay with it.
“But there’s ones like the derby where I fall into a big hole and I can’t manage to stay with the intensity of the game."
Kirchhoff played 84 minutes of the derby against Newcastle United, but his work rate was not in doubt, with The BBC reporting that he ran more than 10 kilometres during the course of the game.
After a poor debut against Tottenham, Kirchhoff has been much improved, excelling in a midfield role shielding the back four, impressing in a win over Manchester United and draw with Liverpool.
The 25-year-old will no doubt have been training hard over the international break to try and resolve the issue, and has a big game upcoming this weekend in which he will want to see a noticeable improvement.
Sunderland host West Bromwich Albion, desperate to pick up a victory and haul themselves towards safety. The Black Cats are currently in 18th place with eight games remaining.