Schalke striker Franco Di Santo apologised for the nature of his departure from Bundesliga rivals Werder Bremen, with fans unhappy with the Argentine's exit.

Di Santo made his debut in a Schalke shirt in a 0-0 draw with Porto in their penultimate pre-season friendly before their Bundesliga campaign begins on August 14 at Werder.

The 26-year-old tried to smooth the waters with Werder - who made 6million on the player after he came to Germany as a free agent after three seasons at Wigan - after the hit-out at the Heidewaldstadion.

Bremen director Thomas Eichin was quoted as saying he was "anything but impressed" by the swiftness of Di Santo's departure, which will make for an interesting reception if Di Santo runs out at the Weserstadion in little over two weeks' time.

"I understand - as a supporter you always want to keep the players you like and I understand that situation," Di Santo said.

"But on the other hand, I did a lot of good things for Werder. I came for free and now they have six million. If it's enough or not, it is six million.

"But I really understand the supporters. It is a job and with a job you always want to improve - every single one of you, not just football players, in every single job in the world.

"If they are angry, I can only say sorry for that. But I am really, really thankful for Werder Bremen to give me the opportunity to be here right now."

Di Santo said he was pleased with his output on debut, adding Andre Breitenreiter's men are capable of competing for trophies - with the DFB-Pokal win in 2010-11 Schalke's only major success in a decade.

"I am really happy. I think because of the performance of the team we deserved to win the game and personally I tried to do my best," he said of Schalke's pre-season outing.

"I can't say if it was perfect or not, but I am happy.

"I expect what every single team like Schalke expects - fight for titles and do our best as a team and as players, because it is one of the biggest teams in Germany, because I have the chance to play in the Europa League and that's it."