Chris Robshaw and Mike Brown are doubts for England's Six Nations opener against Italy, while Henry Slade will miss around four weeks, head coach Eddie Jones has confirmed.
Back-rower Robshaw is contending with a back issue and full-back Brown is suffering with blurred vision.
And Jones described the duo as "borderline" for the trip to Rome on February 4.
"Chris Robshaw would win any sort of water Olympics at the moment. He's unbelievable in the pool," he told the media at the Six Nations launch on Wednesday.
"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 [Wednesday] and we'd be hopeful that by the middle of next week he'd be alright to train. He's also borderline for Italy."
Centre Slade was forced to miss a training camp in Portugal due to a shoulder injury and is set to miss a significant portion of the tournament.
Jones added to Sky Sports: "Slade has got a reasonably significant shoulder injury so he will probably miss at least the first four weeks of the tournament."
Front-rower Kyle Sinckler is another name on an England injury list already containing powerhouses Billy Vunipola and Nathan Hughes, who will miss the entire Six Nations.
"Sinckler was being examined this morning but the likelihood is he has a hamstring injury of significance and is out for six to seven weeks," Jones said.