The European Union (EU) envoys and the US embassy in Tanzania have condemned Monday's attack on the country's opposition leader Freeman Mbowe.
The Chadema party leader was attacked and injured by unknown people in the capital, Dodoma while returning home.
His party said he was being treated at a hospital.
The US embassy, in a statement, said it was "shocked and appalled" by the attack and has called for an investigation on the incident.
It said the attack was the latest in "a long series of disturbing acts of violence and harassment perpetrated against members of the opposition".
The EU envoys termed the incident as an "attack against democracy".
"With general elections only a few months ahead of us it is essential to let democracy take its course and ensure all conditions to full participation incredible and transparent elections," they said in a statement.
Mr Mbowe has been critical of President John Magufuli's response to the coronavirus pandemic, accusing him of promoting policies that could harm the health of Tanzanians.