Rafael Nadal admitted that it will be "hard to return to the practice court" after a shock semi-final defeat by Fabio Fognini ended his bid for a record-extending 12th Monte Carlo Masters title on Saturday.

The 32-year-old said he played "one of my worst matches in 14 years on clay" in losing 6-4, 6-2 to Italian Fognini, having been forced to save three match points at 5-0 in the second set.

It was world No. 18 Fognini's fourth career win against Nadal in 15 encounters and his third on tennis' slowest surface.

Nadal has struggled with knee injuries this season and was playing his first event since withdrawing before an Indian Wells semi-final against Roger Federer last month.

"I lost an opportunity in a very important event for me. I'm sad for that," said the Spanish great, "there was little chance for me to start the clay-court season in a perfect way."

The "king of clay" is yet to win an ATP title this season. The last year he reached May without a tournament victory was in 2004.

The 17-time Grand Slam champion starts his Barcelona Open title defense on Wednesday, as he also fights to keep his world No.2 ranking before the French Open gets underway next month.

Fognini will face unseeded Serbian Dusan Lajovic in Sunday's final – the first time since 2004 that neither Nadal, Djokovic nor Roger Federer have made it to the last day in the Principality.