Dortmund boss promises new signings

"We will invest significantly for next season, but we will do it without having to take out extra money," he told German broadcaster Sport1, referring to the 40 million euros (US$52m) Dortmund have earned so far in the Champions League.

"We will try to get a bit more volume to our forward positions and out wide."

Having drawn 2-2 in Donetsk three weeks ago, Dortmund host the Ukrainian champions at Borussia's Signal Iduna Park stadium on Tuesday in the return leg with a place in the Champions League quarter-finals at stake.

With Dortmund striker Robert Lewandowski having said he will not renew his contract, which expires in June 2014, Watzke said he hopes to retain his services until then with the Poland star having been linked to rivals Bayern Munich.

"My wishful thinking is that Robert will also play for us next season," said Watzke, Dortmund's chief executive officer, but Borussia may be forced to sell their star asset at the end of the season or risk losing him on a free transfer.