Five things we learned this weekend in Bundesliga

Only quick-thinking from VfB Stuttgart's team doctor saved the life of captain Christian Genter in their 1-0 win over Wolfsburg.

Liverpool-bound Naby Keita earned a red card in RB Leipzig's 2-2 draw at home to Borussia Moenchengladbach while newly-promoted Hanover 96 went top of the league for 48 hours, but most hardcore fans left early.

Here are five things we learned from the fourth round of German Bundesliga matches:

Gentner's horror injury

Stuttgart captain Christian Gentner is unlikely to play again this year after fracturing his eye-socket, nose and upper jaw in a horror collision which could have ended in tragedy after he swallowed his tongue.

Wolfsburg goalkeeper Koen Casteels smashed his knee into Gentner's face while challenging for the ball on 85 minutes.

The ex-Germany midfielder swallowed his tongue, which was pulled out of his throat by Stuttgart's quick-thinking team doctor.

"I came out (of the goal), looking at the ball," said Casteels. "Unfortunately these things happen. My left knee came up when I jumped for the ball and 99 percent of goalkeepers do the same."

Robben's clear message

Bayern looked impressive in their 4-0 home romp against Mainz, but tensions are still bubbling.

Thomas Mueller scored their early first goal before Arjen Robben tucked away their second on 23 minutes.

But Robben chose to celebrate with substitute Franck Ribery, ignoring coach Carlo Ancelotti, who benched Mueller in Tuesday's Champions League win over Anderlecht.

Robben's post-match comments were a clear message in Ancelotti's direction: Ribery and Mueller must play and not left on the bench.

"I am proud to played alongside Franck for eight years," explained Robben. "He does the club a lot of good and we need him to win titles.

"Thomas was the key to our success, when he is on, we have a lot more movement in our game."

Nagelsmann rumours

There are rumours that Bayern's next manager will be Hoffenheim's 30-year-old coach Julian Nagelsmann.

The rumour mill says Nagelsmann, who is under contract until 2021, will go to Bayern in 2019 for around five million euros ($5.9m).

However, his agent Marc Kosicke says there is no release clause in his contract.

"I usually don't comment on the details of a contract, but in this case I'll make an exception, because I am not aware there is a release clause in his contract," Kosicke revealed to Germany daily Bild.

"Julian will definitely stay in Hoffenheim for the next two years."

Keita sees red 

Liverpool-bound Naby Keita brushed off a groin injury to play in Leipzig's 2-2 draw at home to Borussia Moechengladbach, but was sent off for kicking Christoph Kramer in the face.

Keita challenged Kramer for the ball, but his out-stretched leg made contact with the Germany international's face.

"I didn't expect the foot to come in so high," said Kramer. "It looked worse that it was, the lip was hit, but no teeth."

Keita is now suspended for Tuesday's match away to Augsburg.

Ultras walk out at Hanover

Hanover's victory over Hamburg put them top of the table for 48 hours -- the first time since September 1969 - but few of their hardcore 'Ultra' fans saw the final whistle.

Hanover's Ultras are annoyed that president Martin Kind wants a controlling interest in the club.

Cries of "Kind out!" were heard throughout Friday's win and the Ultras block was virtually empty on 90 minutes.

"What I found really stupid is that the Ultras left the stadium while the boys were celebrating in front of our fans," fumed Hanover coach Andre Breitenreiter.

"That is a clear signal against the team."