The ranks of the country's top 3-year-olds are rapidly being depleted.

On Sunday Conquistador Cielo, who recently was syndicated for a record $36.4 million, was retired to stud. Today, trainer Howard Tesher indicated that Gato del Sol would be sidelined indefinitely.

Tesher said the Kentucky Derby winner has "a very sore left knee" and that he may have to undergo surgery. "We're going to look at some X-rays for any damage to the knee," the trainer said. "The area is very sensitive to the touch and it has to concern me. An operation is being considered but we have to be certain about the extent of the injury." Gato del Sol finished last in Saturday's Travers Stakes and Tesher theorizes that the injury occurred during the race.

While two of the winners of this year's Triple Crown events won't be seen in the fall, the colt who had been expected to dominate those races is returning to action. Timely Writer, who was the future-book favorite for the Derby until he suffered a near-fatal intestinal illness in April, won his return to competition at Suffolk Downs recently and will continue his comeback at Saratoga on Tuesday.

He is entered in a seven-furlong allowance race here, against competition that appears weak, but he may be running into an ambush. Of his six rivals, only Top Avenger has early speed. The colt won his last start at Monmouth Park, six furlongs in 1:09 1/5, and he should be able to take an easy early lead.