The pair were stretchered off during the latter stages of last weekend’s 2-2 draw at Sunderland, and are both now set for an extended spell on the sidelines with ankle ligament damage.
“They’ve confirmed serious injuries, both ankles,” said Perez. “Probably they are ruled out for six to eight weeks.
"We are trying to accelerate their recovery, and the medical staff prepared different strategies to try to recover the players as soon as possible.
“But for some weeks both are out.”
The Croatian Football Association had earlier this week reported that Lovren was due to be out for three to four weeks.
However, the problem has now been revealed to be more serious than that.
Perez himself admitted that Saints had not initially expected the centre half’s injury to be as bad as Ramirez’s.
“We expected a minor injury from Dejan Lovren and more serious for Gaston, but at the end they have similar injuries – damage of ligaments,” he said. “But we hope to recover them as soon as possible.”