Aljunied GRC MP Low Thia Khiang was discharged from hospital on Thursday after a 21-day stay, following a fall at his home last month, said the Workers' Party (WP).
In a Facebook post yesterday, the party said its 63-year-old former secretary-general is now on hospitalisation leave.
"He is recuperating at home and undergoing rehabilitation," it added.
Mr Low was injured in the head from the fall on April 30, and warded in the intensive care unit (ICU) of Khoo Teck Puat Hospital.
He was transferred to a general ward on May 4 after five days in ICU.
"Mr Low and his family wish to express their thanks to the staff of the ICU and Ward A82 of Khoo Teck Puat Hospital for their dedication and professionalism during his stay," the party said.
In his absence, the other Aljunied GRC MPs have been covering his constituency duties, assisted by former Non-Constituency MP Gerald Giam.
Mr Low is the longest-serving opposition MP in Singapore.
He entered politics in 1988, losing in his first outing as a WP candidate in Tiong Bahru GRC.
He won the Hougang single-member seat at his second election in 1991, and has been an MP since.
Mr Low took over as secretary-general of the WP from Mr J.B. Jeyaretnam in 2001 and went on to lead the party for 17 years.
He stepped down as secretary-general in 2018 and was succeeded by Mr Pritam Singh, an MP for Aljunied GRC.
Mr Low is credited with being the first opposition leader to win a group representation constituency when the WP team he led won Aljunied GRC in 2011.