Jerome Boateng could be available for Germany's second round Euro 2016 match against Slovakia, with assistant coach Marcus Sorg "optimistic" about the defender's fitness.

Boateng was substituted with a muscle injury during Germany's final group match, a 1-0 win over Northern Ireland, but Sorg revealed that the Bayern Munich centre-back is improving.

Should Boateng be unavailable, Shkodran Mustafi could return to the Germany defence after scoring in their group opener against Ukraine, which Mats Hummels missed.

"His muscular induration is getting better," said Sorg. "The medical staff and Jerome are working on it.

"We are all very optimistic, but I'm not a prophet. We all hope that it works out and will do everything for it."

Germany's other main selection dilemma for the last-16 clash surrounds the central striking role, which Mario Gomez took for the Northern Ireland game, scoring the only goal of the match, with Mario Gotze moving wide after operating as a false nine against Ukraine and Poland.

"It's a little more complex [to say who will play]," assistant coach Thomas Schneider said. "Mario Gomez is a player who likes to go in the box and comes from the last row of the defence.

"Mario Gotze is someone who can move in small spaces and who can also attract several players. One could see that they can also play together. We have a lot of options there."

Leroy Sane has yet to make an appearance at the finals but speculation about his future has made headlines, with Manchester City reportedly interested in signing the Schalke winger.

"In the end the player needs to decide [if he wants to decide his future during Euro 2016]," Schneider said of the 20-year-old.

"For us it's important that the player brings good performances in the training and also in the game.

"Probably the whole topic can't be avoided, but we still have the feeling that Leroy is highly focused on the training. If he talks with the coach some time I don't see a problem."

Sorg noted Sane's pace could be an asset for Germany in the knock-out rounds despite the youngster's lack of game-time so far.

"Leroy has his qualities," said Sorg. "If he has some space, if he can surprise the opponent with his speed. 

"It depends on the situation, the requirements are changing: the next games are all-or-nothing-games, you need to risk more."