Barca were unable to register a new contract for Messi when his previous deal expired under LaLiga's strict financial salary limits, leading to him joining Paris Saint-Germain on a free transfer.
Speaking in an interview with Sport on Sunday, Tebas blamed Barca's rejection of the €2.7 billion investment deal with CVC Capital Partners for not keeping hold of the Argentina captain.
Laporta responded to Tebas' claims on Barca TV and said: "I believe his comments are improper of the league president.
"Instead of looking for harmony and understanding, he always looks for conflict and confrontation. He has a sick obsession to see how he can harm Barca and its values, but we Catalans already know him."
Laporta also added Messi could have stayed at the club if Tebas had been more flexible regarding fair play.
"He says that Messi has not stayed at Barça, but he has been the lead actor regarding not staying because of his excess of zeal," he said. "The rest of the leagues have been more flexible [with respect to fair play] and have been able to keep their most relevant players."
He also added that Messi's departure from the LaLiga was "painful" and said he deserved to be treated better from Barca.
"Just as when Cristiano Ronaldo, [Pep] Guardiola or [Jose] Mourinho left, we knew that one day this would happen," he said.
"We've been lucky to have had the two best footballers in the world in the two best teams in the world and LaLiga has been able to take advantage of that and be at the forefront worldwide.
"Perhaps Messi's departure is more painful because I personally consider him the best in the history and he didn't deserve to go like this, not just from Barca but from LaLiga."
Koeman said in an interview with NOS at the weekend that he didn't like comments made by Laporta suggesting the Dutchman did not have full control over playing issues.
However, despite confirming they have had their "issues," Koeman said there was no rift between him and the president.
"Our relationship is good," he said in a news conference. "If there's anything, we speak. We both want the best for the club -- the club is the most important thing.
"There are things we speak about, but there's not a single problem with the president. He comes [to the training ground] often and we speak about things to do with the club. I have no complaints. We've had some issues, but we've spoken and drawn a line under them."
Koeman's Barca side face an early test in the post-Messi era against Bayern. Memories of the German team's 8-2 win in the Champions League in August 2020 are still fresh, but the coach insists it will be different this time.
"More than a year has passed," he added. "Several players still here suffered a lot in that game but now we have a unique opportunity. We can do damage to Bayern, we have a good team.
"We have made some big changes to the team and we need time, but in football you don't have much time. You have to prove yourself. It will be an interesting game and one we can draw good conclusions from about where we are against a powerful rival."
Barca also announced on Monday that striker Martin Braithwaite is set to undergo knee surgery and faces a lengthy spell on the sidelines.
The 30-year-old has started all three of Barca's LaLiga games this season and scored twice in the 4-2 defeat of Real Sociedad in their opening game but sustained a knee injury in the 2-1 win over Getafe on Aug. 29.
He subsequently missed Denmark's World Cup qualifiers and remained in Barcelona but the club said in a statement he had opted for surgery after the injury did not respond to conservative treatment.
Braithwaite's injury adds to Barca's shortage in attack, with new signing Sergio Aguero still waiting to make his debut after injuring a calf tendon last month.