Kei Nishikori, who retired in his opening match at the Barcelona Open on Wednesday, is more confident in his form of late, but acknowledges that the slow surface is not the best for his oft-injured wrist. At last week's Monte Carlo Masters, the kickoff to the European clay-court swing, the 28-year-old posted his best performance since returning to tour from a wrist injury.

Nishikori lost to Rafael Nadal in the Monte Carlo final, 6-3, 6-2, and retired after losing the first set of his match against Guillermo Garcia-Lopez in Barcelona. The hope is that this is not a long-term injury.

“I think it's more pain, especially playing on clay you got to use your wrist a little more. You got to hit more spin,” Nishikori said at Monte Carlo. “Automatically you've got to hit spin. I think it makes little tougher than hard court. That makes my wrist hurt little bit.

"I got to check every week, every day. It's not 100 percent yet, so...I think little pains, it's not just my wrist. It's my hands, my arm, everywhere. I got to take care every week.”

Match point from Nishikori's win over Cilic in Monte Carlo:

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Nishikori withdrew from the Australian Open and began his comeback by playing two Challenger tournaments, winning the second event in Dallas. At the ATP level, he reached the semifinals at the New York Open, but then won just one more match between the Mexican and Miami Opens, before switching to clay.

Nishikori took a couple of weeks off before arriving in Monte Carlo. The world No. 22 took down Tomas Berdych in the first round and then won three three-setters against Andreas Seppi, No. 3 Marin Cilic and No. 4 Alexander Zverev before falling to Nadal.

But he still saw the week as a big step in his comeback.

“I just need some more confidence. Well, for sure this week going to help a lot with my confidence,” Nishikori said in Monte Carlo. “Playing with top players—Tomas, Cilic, beating Sascha [Zverev] yesterday too. That gives me a lot of confidence.

"Tough day today playing Rafa. He was little too good. But I think I've been playing well, this week, and I think I'm almost there. Yeah, just keep believing myself, keep playing tough.”

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Fresh off clay run in Monte Carlo, Kei Nishikori retires in Barcelona

Fresh off clay run in Monte Carlo, Kei Nishikori retires in Barcelona

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