The French champions play Bordeaux on Sunday, one week after their embarrassing 3-1 defeat by Ligue 2 leaders Evian Thonon Gaillard in the French Cup.
Didier Deschamps' men lie in fifth place on 29 points, three points adrift of leaders Lille, and will need a refreshed Gignac to help them defend their title.
"I know that these first six months have not been brilliant and that I did not do everything I should have done," Gignac told reporters.
"I wasn't as professional as I used to be. On a lot of small details. I talked about it to the club, to my family. I have nothing to hide.
"Things were much worse at Toulouse my first season there. But I am strong," he added. "What affects me the most is the Velodrome (stadium). There are a lot of expectations from my club but also from the supporters. I wasn't up to it."
"At Toulouse, the team played for me, I was alone up front. At Marseille, we have a lot of attacking players that I need to adapt to."
"It is up to me to improve technically", he said.
Two seasons ago, Gignac was enjoying the time of his life at Toulouse, scoring 24 goals and emerging as Ligue 1's top goal-scorer.
"I am convinced this club is made for me. I can't not succeed here. Otherwise I wouldn't have come. I had other proposals. I rarely doubt," he said. "I love this city and this town too much to stop at failure."
