Coach Thomas Tuchel says Borussia Dortmund are poised for activity in the January transfer window with Mainz's goal-scoring midfielder Yunus Malli rumoured to be set to join the Bundesliga giants.

Malli, a Turkey international, has scored eight goals in 17 games as a centre forward for Mainz, playing just behind Japan striker Yoshinori Muto, and is reported to be set to cost Dortmund around 11 million euros ($11.9m) from Tuchel's former club.

Dortmund are second in the Bundesliga table, eight points adrift of leaders Bayern Munich, ahead of their first league game of 2016 at Borussia Moenchengladbach on Saturday evening, but Tuchel is looking to add to his squad.

"We are definitely looking, but we need patience and optimism," he said.

"The decisive factors are the depth in the squad, the competition and a certain class of player. I am an advocate of 17, 18 players, all of whom are at a high level."

Tuchel has a few injury concerns with left-back Marcel Schmelzer out with a leg injury, while midfielder Sven Bender has a foot injury and Nuri Sahin is struggling for fitness after injury.

Schmelzer is only expected to feature in Sunday's friendly against second-division Berlin side FC Union.

Tuchel admits his side's 4-0 home win over Borussia Monchengladbach last August will have little relevance given Gladbach's resurgence under new coach Andre Schubert.

The Foals have lost just one of their 12 league games since Schubert took charge and they are now fourth, having been bottom prior to Schubert's appointment.

"Saturday's game is going to be nothing like the reverse fixture," Tuchel said.

"Gladbach have transformed since then, not only but also because of the change in coach.

"They are much more active, aggressive and run more under Schubert, so we expect them to be very courageous."

Only league leaders Bayern Munich have picked up more points than Gladbach in their last 12 matches.

Bayern coach Pep Guardiola said in Thursday's press conference that Dortmund are among "the top five teams in Europe", something which makes Tuchel wary.

"Praise from Bayern is always a dangerous thing," said Tuchel, who said he is more concerned with holding on to second place in the league -- Dortmund are six points ahead of third-placed Hertha Berlin -- than chasing down Bayern.

"Besides, Bayern have a comfortable lead. We are not concerned with that at the moment."