Haller, who scored 34 goals for Dutch champions Ajax Amsterdam last season, was diagnosed during a pre-season training camp in July
Sebastien Haller said he was relieved to finally make his first appearance in a Borussia Dortmund shirt following two surgeries and four rounds of chemotherapy for testicular cancer which sidelined the Ivory Coast forward for six months.
Haller, who scored 34 goals for Dutch champions Ajax Amsterdam last season, was diagnosed during a pre-season training camp in July - weeks after he had been signed for an initial fee of 31 million euros ($33.25 million).
The 28-year-old returned to training earlier this month and finally made his unofficial debut as he came on in the second half of Tuesday's friendly with Fortuna Dusseldorf, which Dortmund won 5-1.
"It was a great moment on the pitch. I got a lot of applause and a lot of messages, I spoke to my team mates and the opponent. This support contributes to performance," Haller said.
"I wanted to be there from the first game. We talked about what is the best solution to get some minutes. After six months, I finally wore a Dortmund jersey for the first time.
"I was really looking forward to playing because I couldn't do it straight away after my move. Playing is a much better feeling than exercising and running through the woods, I missed that feeling."
Dortmund coach Edin Terzic said the team were proud of Haller's comeback.
"It was a very special moment for Seb and his family, but also for us. It was the first time that he wasn't wearing a training shirt but the Borussia Dortmund jersey," Terzic said.