Ivorian and Borussia Dortmund striker Sebastien Haller has returned to training after undergoing testicular tumour treatment.

"Happy New Year to all! And it's off to a great start for me because it means getting back on the field," the 28-year-old Ivory Coast international wrote on Twitter, posting images of himself working out at the gym.

"2022 wasn't the easiest year but it prepared me for all the new challenges that 2023 will bring."

Haller will initially undertake strength and conditioning work, as well as some light ball drills, with a view to making his competitive comeback - and long-awaited Dortmund debut - during the second half of the 2022/23 campaign.

"It's very positive for everyone that he is back," commented Dortmund sporting director Sebastian Kehl.

"We gave him the best possible support as a club, but, at the end of the day, it was down to his great efforts."

German side Dortmund signed Haller for an initial fee of 31 million euros during the close season after the striker scored 34 goals last season for Dutch champions Ajax.

Dortmund said Haller would be "carefully introduced" back into the team.

The club are sixth in the Bundesliga, nine points behind leaders Bayern Munich. The season resumes later this month, with Dortmund taking on Augsburg on Jan. 22.