Poland international Lewandowski was shown two yellow cards in the first half of Barca's last match before the FIFA World Cup break – a 2-1 win at El Sadar on 9 November (AEDT).
The Spanish Football Federation (RFEF) issued Lewandowski with an extended three-game ban for an alleged gesture made towards referee Gil Manzano after being dismissed.
It was announced on Saturday (AEDT) that Barca was unsuccessful with its latest appeal against the suspension, and Lewandowski has questioned the severity of the punishment.
"It's difficult because I feel that three games is too much for what I did, that's for sure," he said. "It's painful not to be able to play three games because of that."
Former Bayern Munich striker Lewandowski insists the gesture that landed him in trouble was in fact aimed at head coach Xavi.
"Nothing happened with the ref," Lewandowski said. "The reason I got three matches was nothing to do with the referee, it was to do with me and the coach. That's all I can say.
"One or two weeks before, I had a chat with Xavi, and he told me that I had to watch out if the referee gave me a yellow card.
"That was just a gesture to express he couldn't understand what was going on. We had talked about it, and it was something between Xavi and me. I didn't understand anything."
Lewandowski has 18 goals in 19 games this season – only Kylian Mbappe (19) and Erling Haaland (24) have scored more among players from Europe's top five leagues.
The 34-year-old has continued his prolific goalscoring form in a new country and is hopeful of adding to his trophy collection during his time in Catalonia.
"I will stay at Barcelona as long as I am fit and hungry for titles," he said. "We have to have the mentality of a champion."
Barcelona resumes its LaLiga campaign with games against Espanyol and Atletico Madrid either side of facing third-tier side Intercity in the last 32 of the Copa del Rey.