A spokesman for Lord Rennard, the party’s former chief executive, said he had instructed a QC specialising in public law to advise him on the decision to launch a second inquiry into his conduct.
It follows the announcement on Monday that Lord Rennard was being suspended from the party pending an investigation into claims that he brought the Liberal Democrats into disrepute by his refusal to apologise to four women activists who alleged that he sexually harassed them.
The peer was ordered to issue the apology by Lib Dem leader Nick Clegg, after an earlier inquiry by Alistair Webster QC concluded that the women’s claims were credible, but there was insufficient evidence to bring disciplinary charges.
Mr Webster’s report also recommended that Lord Rennard apologise to the women who had complained.
Supporters of the peer dismissed the latest inquiry as no more than a “rerun” of the first.
Lord Rennard’s spokesman said: “A senior QC specialising in public law matters has been instructed and is advising Lord Rennard as to the lawfulness or otherwise of the decision to hold a second inquiry.”
The latest move will fuel speculation that Lord Rennard – who has always denied the allegations against him – could now seek an injunction blocking the inquiry.
With one of the women he is alleged to have harassed refusing to rule out a counter-claim against the peer, the Lib Dems are faced with the prospect of becoming embroiled in a series of damaging court battles that have the capacity to drag on for months.
Friends of Lord Rennard insisted that he did not want the case to end up in the courts, but claimed that attempts to resolve the issue through mediation had been blocked by Lib Dem president Tim Farron.
Earlier, former Liberal Democrat leader Lord Ashdown appealed to Lord Rennard to end the turmoil gripping the party and issue an apology.
Lord Ashdown, who described himself as a “friend and admirer” of his fellow peer, said it would “cost him nothing” to say sorry for any offence he had caused.
Lord Rennard has refused to apologise, in part because of warnings that, by doing so, he could leave himself “defenceless” in the event of a civil action against him.
However, Lord Ashdown insisted that he could apologise for any offence he may have given without compromising his legal position.
He said: “It is very easy to do. No one is suggesting that Chris [Lord Rennard] should put his own innocence, as he claims it, in jeopardy.
“If it is the case – this is what QC Webster asserted – that offence has been given, it costs him nothing to say, ‘If inadvertently I have caused you hurt, I apologise for that’. It’s done every day. It is the very heart of mediation.”
The row over Lord Rennard’s treatment has opened up bitter divisions within the party, with his supporters claiming he has been subjected to a kangaroo court, while critics have argued that swifter, tougher action should have been taken against him.
Lord Ashdown acknowledged that it had not been the Liberal Democrats’ “finest hour”, but he strongly defended Mr Clegg’s handing of the case, saying there had been no other course of action open to him.
“In the end, the issue that Nick has stood on with great courage and in the face of great flak from the press and indeed some in the party too, is an important issue, an important principle, and he is right to do so,” Lord Ashdown said.
Former Liberal leader Lord Steel said most party members would be “horrified at the mess being made of this at the centre of the party”.
Meanwhile, Mr Clegg’s former special adviser Bridget Harris, who is one of the women Lord Rennard is alleged to have harassed, and who resigned from the party when the decision was made not to discipline him, has not ruled out suing the peer, although she said that any legal action would “depend on the circumstances”.