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World number one Andy Murray said he is 'concerned' following defeat by Borna Coric in last 16 of the Madrid Open, but denied being low on confidence.

Murray was beaten 6-3 6-3 by Coric, ranked 59th in the world, on Thursday.

The Briton has endured a tough season on clay, suffering a shock defeat in the last 16 of the Monte Carlo Masters last month and also losing in the semi-finals of the Barcelona Open.

"I definitely think I need to be concerned about today," Murray said.

"It's not always the worst thing losing a match, but it's sometimes the manner of how you lose the match which can be concerning or disappointing."

Coric, 20, only gained a place at the tournament after Richard Gasquet withdrew - becoming the first lucky loser to reach the quarter-finals in the Madrid tournament's 16-year history.

The Croat broke his Scottish opponent three times in the opening set, and a further break in the second was enough to secure victory in one hour and 25 minutes.

Top seed Murray hit 14 winners to his 28 unforced errors, but insisted his poor performance was not down to a lack of confidence.

"I was just making lots of mistakes early in the rallies and trying to end points very quickly at the beginning, and the errors just kept piling up." the 29-year-old told ´óÏó´«Ã½ Sport.

"I didn't feel that was down to confidence - I just wasn't focusing as well as I needed to on each point.

"I made a lot of unforced errors and I also didn't find any way to make it a more competitive match, so that's the most disappointing thing for me.

"You can lose matches sometimes, but the manner of today's loss was disappointing."

´óÏó´«Ã½ tennis correspondent Russell Fuller:

This result will come as a shock to Murray's system.

He had seemingly been growing in confidence, and rediscovering his rhythm little by little as he made his way from Monte Carlo to Barcelona, but now has just one week in Rome to find the form and belief which would make him a genuine contender for the French Open.

His first serve, which has been hindered by an elbow injury, was not to blame against Coric, who played aggressively and fluently and took full advantage of Murray's error-strewn performance.