Status Quo has canceled six concerts as guitarist Rick Parfitt battles an undisclosed illness. The group, best known for the 1968 hit 'Pictures of Matchstick Men,' was due for a show tonight in Croatia. Dates through Aug. 10 in Monte Carlo, Switzerland and Germany have also been called off.

Parfitt, the second-longest-tenured member of Status Quo after frontman Francis Rossi, underwent bypass surgery in 1997. Band management confirms the 65-year old has been hospitalized.

"We don't cancel shows lightly as any of our fans will tell you," Status Quo manager Simon Porter says via Facebook. "But in this instance, we have no option but to follow medical advice."

'Matchstick Men,' a No. 7 U.K. hit for Status Quo, was later revived by Camper Van Beethoven -- who topped Billboard's modern rock charts with a 1989 remake. Ozzy Osbourne covered it, too. But Status Quo wasn't any one-hit wonder. 'Ice in the Sun' went to No. 8 in 1968, then 'Down Down' topped the U.K. singles charts in 1975. Their cover of John Fogerty's 'Rockin' All Over the World,' originally the title track for a 1977 Status Quo album, became a concert favorite.

There is no word yet on the fate of future scheduled dates, including a pair in the U.K. later this month. The band is promising more information on Parfitt's condition next week.

Watch Status Quo Perform 'Down Down' Earlier This Year