Aviva attempted to quash suggestions that its proposed buy-out of the RAC was stalling this week.
Only a further 5% of RAC shares have been provisionally sold by the second 'deadline' for acceptances.
A spokesman for the insurer said: "It is not uncommon for there to be acceptances in single figures at this stage, and the deal will still go through. We are very happy with the take-up of our attractive offer."
Just 57% or 67,495,276 shares had been accounted for by the 28 April deadline.
Andrew Hubbard, tax partner at Mazars, said: "The Aviva board will be asking themselves some serious questions now about whether this deal is feasible.
"It may be that they wanted to buy RAC on the cheap and if that can't happen then it is debateable whether they will want to revise it."
Another investment analyst, representing one of the parties involved, said: "It would appear that one of the major shareholders is not convinced. Aviva will be making some frantic calls to make sure this one goes through."
RAC shareholders who have already provisionally accepted the offer can retract their support this week. Aviva has until Friday to revise their offer if they see fit.