Byrne was forced to leave the field two minutes before half time in Saturday's first Test and now faces a race against time to be ready for selection for this weekend's next assignment against the Springboks in Pretoria.
"Lee will have treatment over the next couple of days, but I'm confident he should be fit for the weekend," said Lions head doctor, James Robson.
"You all saw him missing for part of the warm-up on Saturday and that was because he forgot to have his strapping put onto.his left foot. Strange things happen in dressing rooms in the build up to Test matches.
"He was fine before the game, but it is possible he has suffered a mild recurrence of his old injury. He has had problems with some fibres in the arch of his foot, which is a very painful condition that needs treatment.and dressing."
Other than Byrne, the Lions escaped with a pretty small injury list from the first Test battle. Gethin Jenkins had four stitches put into a cut eye, skipper Paul O'Connell had a few teeth loosened, two try hero Tom Croft suffered a slight cal strain and Tommy Bowe strained his elbow.
None of the injuries looks serious enough to rule the players out of contention for Pretoria this weekend, although Andrew Sheridan's back strain has forced the Lions to call up England prop Tim Payne to provide cover.
Ireland's record cap holder John Hayes arrived in Durban on Saturday morning to take over from the injured tight head Euan Murray and is fit to play on Tuesday against the Emerging Springboks if required.