Chris Robshaw and Mike Brown are doubts for the Six Nations opener against Italy as England's injury concerns continue to escalate.
Robshaw has a back problem and Brown is being troubled by blurred vision, leaving Eddie Jones to rate the Harlequins duo as "borderline" for the trip to Rome on Sunday week.
Robshaw was a guaranteed starter in England's back row while Brown was equally assured of his place at full-back and they will continue their rehabilitation at the squad's training camp on the Algarve.
"Chris Robshaw would win any sort of water Olympics at the moment. He's unbelievable in the pool," Jones said at the Six Nations launch in London.
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"He did a water aerobics class with a bunch of Portuguese women yesterday (Tuesday). Apparently he was the best in the class.
"If we play Italy in the pool he'd be all right, but if we're playing rugby then he'd be borderline to get there.
"Mike Brown is starting to do some light skills today (Wednesday) and we'd be hopeful that by the middle of next week he'd be all right to train. He's also borderline for Italy."
England have received more concerning news over Kyle Sinckler, their second choice tighthead prop, who could miss the entire tournament with his hamstring problem.
"Kyle Sinckler was being examined again this morning, but the likelihood is that he has a hamstring injury of significance and will probably be out for six to seven weeks," Jones said.
Jones also revealed that Henry Slade will miss at least the first half of the Six Nations because of a shoulder issue but could have Jack Nowell back from his ankle complaint in time to face Wales on February 10.
England have now seen 16 players ruled out of the start of their title defence, a number that will climb to 18 if Robshaw and Brown fail to recover.
The wave of injuries that has thinned the champions' ranks is mirrored by similar problems encountered by their rivals, but Jones views the crisis as a blip.
"You just have these runs. I don't think it's anything significant. You have ups and downs in the game and at this particular time there are a number of injuries," he said.
"For the Lions players you can understand that the injury risk is high because of the lack of a proper pre-season that they have, but obviously they're not all Lions players."