Robert Lewandowski believes he is not playing enough at Bayern Munich, according to a source close to the striker, who told ESPN FC the Poland international's "rhythm was clearly broken" this season.
Reports over the past months have linked Lewandowski with a move away from Bayern, though CEO Karl-Heinz Rummenigge told reporters earlier this week that the 29-year-old will remain next season.
Lewandowski scored 15 goals as he appeared in all 17 games over the first half of the Bundesliga season, but during the winter training camp, he struggled with a patellar tendon injury, the source said, and returned to training late ahead of the restart after the break.
He has since started seven of 16 possible league games and came off the bench five times, but he scored 14 goals in those 12 appearances.
Winter signing Sandro Wagner, who hopes to be in Germany's World Cup squad, meanwhile, has scored eight goals in 13 Bundesliga appearances, six of them as a starter.
"Robert's rhythm was clearly broken," the source said. "He played almost every game over the past few years [and] even played with a shoulder injury at Real last year and he scored. He played with a face mask against Barcelona in 2015. He does not have this rhythm in 2018."
Lewandowski has come under fire at Bayern in recent weeks for failing to score in the Champions League semifinal defeats against Real Madrid and then denying coach Jupp Heynckes a handshake following his substitution in the 3-1 defeat of Cologne.
Members of the German media made Lewandowski the scapegoat for Bayern's failure to reach their first Champions League final since 2013.
The source said: "It's a team sport. And if in a Champions League semifinal an attacker does not score, that might also be down the quality of world-class players like Sergio Ramos and Raphael Varane."
Heynckes, speaking to reporters at a news conference on Friday, said he was unaware Lewandowski believes he hasn't had enough game time since the break.
"He never told me that he felt he hadn't played enough," Heynckes said. "I have repeatedly heard that we had an extremely stressful and intensive fixture list, therefore I gave him regular breaks with the big games in mind. For example, if he didn't play a game in eight days, that's a normal rhythm and he wouldn't lose any playing rhythm."
Last season, Lewandowski injured his shoulder in the lead up to Bayern's loss to Madrid in the Champions League quarterfinals, missing the first leg and returning for the return despite not being 100 percent fit.
"If he had had got injured again during the decisive phase [this season], then Sandro Wagner would have had to play without any playing time at all," Heynckes said.
"Robert is an ambitious and exceptional striker and has the chance to score 30-plus goals in the Bundesliga for a third successive season. I'm not overvaluing his reaction on Saturday. I understand this. He is a striker who doesn't enjoy being substituted."
Lewandowski scored 30 goals in the last two Bundesliga seasons, and going into the final game against Stuttgart on Saturday, he has scored 29 goals in 29 league appearances.
And, having scored 106 goals in 125 Bundesliga games for Bayern Munich, and a further 74 in 131 top-flight appearances for Borussia Dortmund, Lewandowski has flirted with a move abroad for several years.
Earlier this year, he split from longtime agent Cezary Kucharski and is now represented by Pini Zahavi, who was central to Neymar's world-record move from Barcelona to Paris Saint-Germain.
But, speaking to reporters on Tuesday, Rummenigge said he's "happy Lewandowski is tied to the club on such a long-term deal."
Under contract until 2021, Bayern are not prepared to cash in on the league's top scorer.
"Nobody needs to worry about Robert Lewandowski's relationship with FC Bayern Munich. We have a very good one," Rummenigge said. "We know what we have in him. I am very happy that Lewandowski is tied to the club on such a long-term deal.
"He will still be at Bayern next season."
ESPN FC Bayern Munich correspondent Mark Lovell contributed to this report.