Paris - World No 4 Marin Cilic announced on Friday that he will miss next week's Madrid Open tournament with a knee injury suffered during last month's Monte Carlo Masters.
The former US Open champion was dumped out in his first match in Istanbul by unseeded Tunisian Malek Jaziri on Thursday, having struggled with the knee problem during his campaign in Monaco, where he was knocked out in the third round by Kei Nishikori.
"I began feeling sharp knee pain back in Monaco and while I'm eager to compete, my team and I decided the best option is to pause and focus on rehab," Cilic wrote on Twitter.
The injury casts doubt on the Croatian's participation at the French Open, which starts on May 27.
Cilic, who lost to Roger Federer in both last year's Wimbledon final and January's Australian Open final, reached the last eight at Roland Garros for the first time in his career last year.
He joins the likes of Stan Wawrinka, Roger Federer and Andy Murray in missing the Masters event in Madrid, where world No 1 Rafael Nadal will be a red-hot favourite after winning his 11th Barcelona and Monte Carlo titles.