Borussia Dortmund midfielder Ilkay Gundogan feels he's only working to "60-70 per cent" capacity.

The Germany international has fought his way back from long-term back injury and is courting serious interest from Manchester United and Arsenal.

"I do think that I have set my top standards before my injury. Now it's step by step to get back to my former strength.

"I am glad that I am now physically again in a state that allows me to handle everything," said the 24-year-old midfielder.

With just over a year to run on his BVB deal, Gundogan is expected to leave this summer.