Hendrie Kruzen, assistant to former Borussia Dortmund coach Peter Bosz, has said they could have been more active in the transfer market.

Kruzen, 53, joined Dortmund from Ajax with Bosz in the summer, but the duo were sacked after an eight-game winless streak in the Bundesliga and a disappointing Champions League campaign.

Speaking to Dutch newspaper Tubantia, Kruzen said: "I wish them all the best. There are no hard feelings -- I don't want them to lose.

"I would have preferred to stay. They are one of the biggest clubs in the world -- you have to experience it. At a home game, you really say: 'Wow, Ajax is big, Dortmund is twice as big, there are 81,000 people in the stadium and there is a [season ticket] waiting list of 37,000 people.'"

Bosz and Kruzen tried to implement a very attacking style, with the approach bringing them a five-point lead at the top of the Bundesliga after seven matches.

But their form fell away and Kruzen said: "In the summer we were allowed to buy players but we decided that we wanted to get to know the team first.

"There were Champions League winners, you expect something from that. Ultimately, that approach was too conservative and we had to get players we thought would fit in.

"In the winter break, we would have opted for two central defenders and a striker. That says it all, really."

Hendrie Kruzen joined Dortmund along with Peter Bosz. Jeroen Meuwsen/Soccrates/Getty Images

Kruzen pinpointed the injury suffered by defender Lukasz Piszczek while playing for Poland in October as a turning point, saying: "Even if it sounds strange, it went downhill after Lukasz Piszczek got injured.

"He encouraged his teammates, was enthusiastic, but then dropped out.

"Then I expected more from Sokratis [Papastathopoulos]. He was the vice-captain and had to show leadership. Instead, he left us hanging."

He indicated that the centre-back had not helped the players get on the same page as the coaching staff and said: "The goalkeeper and the defenders wanted a more defensive approach, the midfielders and attackers were pleased with our way and wanted to continue.

"We had a squad of 27 players -- that was too much. You field 11, the rest are almost always dissatisfied, the unrest increased and groups within the team emerged.

"Good results can hide a lot, but once results take a turn for the worse, then everyone focuses on the system and the physical condition of the players."

But Kruzen denied claims that Dortmund's players had not been fit enough and said: "Nonsense -- data doesn't lie. Compared to last year, it was the same or even better."

And he stressed that he was not bitter about his departure from the club, adding: "I do not stay in the negative, never. I've learned things, I'm going to take advantage of that."