Lib Dem leader Sir Ed Davey has said he is "minded" to vote against an upcoming bill to legalise assisted dying.
MPs are due to debate proposals to give terminally ill people in England and Wales the right to choose to end their life.
The bill was introduced by Labour MP Kim Leadbeater after the prime minister said he would allow a free vote - meaning Labour MPs can choose based on their own conscience rather than having to follow the party line.
The issue has split Parliament, with MPs divided by ethics and practical concerns.
Sir Ed - who is also giving his MPs a free vote - warned that elderly and disabled people might feel pressured to end their lives if they felt like a "burden”.
Sir Ed said he was "open-minded" and would listen to the debate, but added he was "very minded" to vote against.
The Kingston and Surbiton MP said he was concerned about the “psychological impact” of legalised assisted dying on elderly and disabled people, largely because of his own mother's battle with bone cancer.
Sir Ed told reporters he administered morphine to his mother to help her deal with the pain of her condition towards the end of her life.
Despite being in pain before she died, Sir Ed said he did not think “she would have wanted" the option to have someone help her take her own life.
Instead of focussing on assisted dying, the Lib Dem leader argued the UK should “do much better” on palliative care.
Better end-of-life care would ease people’s fears of a painful death, making many cases of assisted suicide unnecessary, he said.
Assisted dying generally refers to a person who is terminally ill seeking medical help to obtain lethal drugs in order to take their own life.
Throughout the UK, laws prevent people from asking for medical help to die.
Euthanasia is illegal under English law and is considered manslaughter or murder. The maximum penalty is life imprisonment.
In Scotland, it is possible that helping a person to die could lead to prosecution for an offence such as culpable homicide.
MPs are due to vote on Leadbetter's Terminally Ill Adults (End of Life) Bill on 29 November.
Full details have not yet been released, but bill is expected to be similar to one introduced in the House of Lords in July 2024, which said terminally ill adults with six months or less to live would be able to get medical help to end their own lives.