Rivera -- who had been hobbled by hamstring problems for weeks but felt a pop sliding into third base on Tuesday night and was placed on the disabled list on Wednesday -- has a rupture where the tendon inserts into the knee. Falsone said it is an unusual baseball injury and there's a medical debate whether surgery is appropriate.
She said the tendon is sometimes harvested by surgeons performing Tommy John surgery, who use the tendon as a replacement elbow ligament because another tendon also holds the hamstring muscle in place.
"People function without the tendon," Falsone said.
If surgery is performed, she said, it is not to re-attach the tendon but to debride the area. The injury that forced Kirk Gibson to hobble around the bases on his legendary World Series walk-off homer was a similar tear of the tendon where it inserts into the knee.
"We will re-evaluate after two weeks and see where we're at," Falsone said. "[Rivera] did some exercises today and was pain-free. The best case is that he's ready to return in 15 days, but I don't think that's what we're looking at. The worst case is six to eight weeks. He will play this season, for sure."