“We are taking it one day at a time. It could become better in just a couple of days, it could also take a month,” Swedish team doctor Rene Tour told the Swedish News Agency TT.
Alshammar said at a Swedish team press conference that she has a pinched nerve in her right shoulder.
The 34-year-old is slated to take part in the women’s 4x100m freestyle relay when the swimming kicks off on Saturday.
She’s got a bit more time to recover before her individual events, with the 100m freestyle heats on Wednesday and the 50m free heats on Friday, August 3, the penultimate day of swimming competition at the Aquatics Centre.
Alshammar, a fixture on the international stage since the early 1990s, competed in her first Olympics at Atlanta in 1996.
She earned Olympic silver in both the 50m free and 100m free at Sydney and also competed in Athens and Beijing.
She won the 50m free at the World Championships in Shanghai last year, and put herself among the top 10 in the world this year with a time of 24.50 in the one-lap sprint at the Swedish championships in early July.
Alshammar’s coach Johan Wallberg said her shoulder trouble started after the national meeting. At first she believed it was just transient neck pain, but an MRI on Wednesday showed the pinched nerve.