Bayern Munich defender Mats Hummels has said the defending Bundesliga champions cannot currently be considered one of the best sides in Europe.
"It is definitely the case that internally we have to improve a few things and pull together," Hummels told German magazine Sport Bild.
"Not everything is bad, but things are not at the level they need to be in order for us to be among the absolute top teams in Europe. The cohesion in the squad has to grow again."
Bayern host Celtic in the Champions League on Wednesday eager to put in a good display after their 3-0 thrashing at Paris Saint-Germain three weeks ago.
The shock result led to the sacking of Carlo Ancelotti after 15 months in charge, with 72-year-old Jupp Heynckes, who steered Bayern to the 2013 treble, returning for a fourth spell as coach in Munich.
Bayern are second in the Bundesliga behind Borussia Dortmund after flooring Freiburg 5-0 last Saturday in Heynckes's first match back at the helm.
Hummels: "You can't get on with all of your 22 teammates"
"The small groups must have a good relationship between themselves, which is important," said Hummels. "It is simply not the case that you can get on with all of your 22 teammates in exactly the same way."
Hummels added Heynckes has taken Bayern back to basics with tougher training sessions than the star-studded squad was used to under Ancelotti.
"The first impressions are that Jupp Heynckes is very demanding, he expects a lot from the team," said Hummels. "The training is a little harder, demanding more intensity, which stays at a high level.
"He wants basic things: punctuality, courtesy towards all employees, everyone should be greeted and treated in a friendly fashion, no matter what their task is."