Rainbow Blue, the 2004 Harness Horse of the Year, may have suffered a season-ending tendon injury earlier this week.

“I can’t pinpoint when it happened,” said trainer/co-owner George Teague, who discovered the injury Tuesday. “An ultrasound showed that it was an injury. The prognosis is that she may be out for the rest of the season.”

The four-year-old mare is a perfect 4-for-4 this year, putting her lifetime record at 30-for-32 with $1.4M in earnings.

“The last time I drove her [June 4 at Woodbine] she went 1:49 2/5 like she was going a mile in 2:00,” said Rainbow Blue’s regular driver, Hall of Famer Ron Pierce, “and she could have gone a lot faster.”

When reached, Pierce had not yet spoken with Teague and did not know the full extent of the injury.

Rainbow Blue, who was scheduled to start in the $215,000 Lady Liberty Pace tomorrow night at The Meadowlands, is currently getting stall rest at the Teague Farm in Delaware.