Koeman appeared sceptical about the backing he received and irritated by criticism in the media after one win in four games has left Barca's La Liga title hopes hanging by a thread.
Atletico leads defending champion Real Madrid by two points with two matches remaining and will win the title if it beats Osasuna at home and Madrid fails to win at Athletic Bilbao.
Xavi Hernandez has signed a new contract with Al-Sadd to put an end to speculation linking him to La Liga giants Barcelona.
The nine other rebel clubs reached settlements last week to commit to UEFA competitions and pay millions of euros (dollars) in forfeits of future prize money and donations to a UEFA-run charity.
Barcelona coach Ronald Koeman has admitted that his side lowered its intensity in the second half of the LaLiga clash against Levante.
Barcelona was up 2-0 and 3-2 but couldn't hold on, despite knowing that a win would have put the team provisionally ahead of Atlético Madrid.
Atlético played well at the Camp Nou but couldn't capitalize on its chances, with Luis Suárez unable to break through with a goal against his former club.
The three clubs are the only ones from the original 12 yet to renounce the proposed competition that would guarantee its founding members involvement every season, instead of having to qualify.
Atletico were 10 points clear at the start of February but six wins in 14 games since then have seen that lead reduced to two.
Top seed Nadal, an 11-time champion in Barcelona, eased to a 6-3, 6-2 win over world number 13 Carreno Busta in 90 minutes.
The Super League, which provoked a backlash by other clubs, fans and authorities around Europe, was announced by a dozen top clubs in England, Spain and Italy on Sunday.
Many feel these clubs could face sanctions from UEFA or their respective associations but La Liga president Javier Tebas said that they are in no hurry to take action against these clubs.
Ronald Koeman does not believe Barcelona's involvement in the collapsed European Super League will have an impact on the club's performance in La Liga.
Fognini denied wrongdoing and was upset as he left the court, breaking his racket after hitting it at the net post on his way out.
Roberto Bautista Agut defeated fellow Pablo Andújar 6-4, 6-0 to advance to the round of 16 in the Barcelona Open.