Lionel Messi says his failed attempt to leave Barcelona in the summer has affected his form this season.
In August the Argentina forward said he wanted to exercise a clause in his contract which he said allowed him to leave on a free transfer.
But Barcelona refused, saying his 700m euro (£624m) release clause had to be met.
Messi equalled Brazil legend Pele’s record of 643 goals for a club by scoring for Barcelona in Saturday’s draw against Valencia.
It was Messi’s ninth goal in 17 appearances this season for Barcelona, who are fifth in La Liga.