England are sweating on the fitness of Chris Robshaw and Mike Brown ahead of their Six Nations opener against Italy, with Henry Slade and Kyle Sinckler also sidelined.
Back row Robshaw is struggling with a back problem while fullback Brown is experiencing blurred vision. Both are "borderline" for their match against Italy on Feb. 4.
"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 west London.
"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 all right to train. He's also borderline for Italy."
England are battling a lengthy injury list. Slade and Sinckler added to the sidelined contingent with both missing their pre-championship Portugal training camp.
"Slade is still ongoing, checking of the injury but probably out for three to four weeks. 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 will not call up a replacement for Slade but Henry Thomas has been added to the squad for the sidelined Sinckler.
Jack Nowell is also on the road to recovery from an ankle injury and will likely miss their opener against Italy but should be in contention for their second round game against Wales.