The 27-year-old left Tottenham Hotspur in August after a drawn-out saga that led to Real paying a fee of up to 42 million euros, according to media reports.
"This is a very technical league but also a very demanding one in physical terms," said Modric who has only started 11 games in La Liga.
"Little by little I am getting used to it. I don't like to give myself a mark out of 10 but I'm not entirely happy with my performances so far," he told a news conference.
"In some games I have shown why I was brought here but in others I haven't. I missed pre-season and this has had an influence.
"The coach and my colleagues have had a lot of patience with me. I think the club and the fans will end up being pleased with me."
One positive for coach Jose Mourinho, who has one eye on Wednesday's visit of Manchester United in a Champions League last-16 first leg, was the return to fitness of defender Pepe for the Sevilla game.
The Portugal centre-back, out since the turn of the year due to ankle surgery, has been included in Real's 19-man squad after having returned to training in the week.
