Borussia Dortmund have already tied up deals for Julian Brandt, Thorgan Hazard and Nico Schulz, but Axel Witsel has hinted that there could be more to come.Having missed out on the Bundesliga title to Bayern Munich in 2018-19, Lucien Favre is determined to ensure that his side are better placed to sustain a challenge next term.He already has plenty of quality on his books in the form of Witsel, Jadon Sancho, Marco Reus and Paco Alcacer. Article continues below Editors’ Picks ‘There is no creativity’ – Can Solskjaer get Man Utd scoring freely again? ‘Everyone legged it on to the pitch!’ – How Foden went from Man City superfan to future superstar Emery out of jail – for now – as brilliant Pepe papers over Arsenal’s cracks What is Manchester United’s ownership situation and how would Kevin Glazer’s sale of shares affect the club? Reinforcements are required, though, and Dortmund have moved early in the window to get fresh faces on board.Witsel is impressed with the ambition being shown, but believes that further funds could be invested before the end of the summer.The Belgium international midfielder told BILD: “We’re stronger now we’ve got Julian Brandt, Thorgan Hazard and Nico Schulz.“I played against Brandt in Leverkusen, it was hard work. I’m delighted for Thorgan, too; he’s only going to get better, but they’re all good transfers. We need them, and perhaps there are more on the way.”Dortmund appeared well placed to secure domestic dominance last season, only to suffer an untimely wobble.Witsel said of that experience and how it can serve the club well: “We gave away too many points during the second half of the season, but we’re a young team.“It was still a positive experience because we played a brilliant season. Nobody expected it from us. Now we have to learn from the experience.”Everyone at Signal Iduna Park is determined to right the wrongs of 2018-19 next season, with Witsel confident that Dortmund will be back in contention for major honours at home and abroad.He added: “We want to play an even better season next term.“We’ve got young players, but experienced guys, too. You need that in a title race.“We can win titles and cups, anything is possible!”Witsel returned to European football from China in the summer of 2018 and committed to a four-year contract at Dortmund, with the 30-year-old buying into a long-term project.