Bayem Munich's record signing Lucas Hernandez took part in his first squad training session on Tuesday, four months after a serious knee operation, the Bundesliga champions reported on their website on Wednesday.

The 23-year-old French World Cup winner has yet to feature for Bayern since his 80 million euro ($89 million) move from Atletico Madrid in March.

His medical showed damage to the medial collateral ligament in his right knee that required an immediate operation.

Hernandez is unlikely to be ready for the opening game of the season against Hertha Berlin on August 16 but it is good news for his new teammates and manager Niko Kovac.

"I think the most important thing for the time being is that he's properly fit and starts to settle in," German international Leon Goretzka told the Bayern website.

The defender's return coincides with a media broadside aimed at the club by

striker Robert Lewandowski who has called on Bayern to bring in at least three new players.

"In attack we lost three players in the shape of Franck Ribery, Arjen Robben and James (Rodriguez)," Lewandowski told Sport Bild on Wednesday.

"And for the moment we have no new recruits for these positions."

While Robben has retired, Frenchman Ribery is out of contract and seems likely to be heading to Saudi Arabia while James has come to the end of a two-year loan period and has returned, for the moment at least, to Real Madrid.

Veteran defender Rafinha has also left in order to return to Brazil.

So far this summer, Bayern have only reinforced their defence with French world champions Hernandez and Benjamin Pavard while promising 19-year-old striker Jann-Fiete Arp has arrived from Hamburg.

The German champions have also been trying for weeks to attract Leroy Sane from Manchester City but no announcement has yet been made.