Ramirez strained his right hamstring while running from the bullpen to the mound to celebrate Johan Santana's no-hitter on Friday.
Reliever Pedro Beato is eligible to return from the 60-day disabled list, but he will not be recalled until he makes a few more rehab starts. Collins said there is no room for him on the 40-man roster at this point.
"There's too many other things right now," Collins said of Beato's return. "He pitched very well yesterday. His velocity was better than it has been. I think his arm strength is coming back, but he needs a few more outings."