Rocard, an 81-year-old Socialist veteran, will likely remain in hospital for a few days the French foreign ministry said on Saturday.
The former PM fell ill on arriving at the French embassy, but was reported to be conscious and was visited in hospital by the French ambassador who spoke with him, the ministry said.
“It’s possible that Swedish doctors will want to keep him under observation for a few days,” the ministry added.
It had been hoped initially that Rocard would be allowed to leave hospital already on Friday evening.
Spokesperson Bernard Valero confirmed on Friday evening that Rocard had been taken to intensive care.
Friends denied French media reports that Rocard had had a stroke.
Rocard was a leading figure on the French left for more than three decades, serving as prime minister under President Francois Mitterrand, despite the pair’s personal political rivalry.
He remained active in politics until very recently, serving as a member of the European parliament until 2008 and advising current centre-right President Nicolas Sarkozy on a national loan project in 2009.