FTSE100 closed lower as markets swirled with uncertainty and as small cap pharma firms did well.
Traders were also put off by continued fears over a potential Fed interest rate rise.
The blue chip benchmark closed 1.82% down to 6,053, while the FTSE AIM100 lost 0.17% to 3,357 and the FTSEAIM All share was down 0.23% to 723.480.
The private equity group would have to pay as much as 500p to take out the group, said the reports.
Restaurant Group’s share price slumped last month after a profit warning.
The Frankie & Benny’s, Chiquito and Garfunkel’s owner indicated year pre-tax profit would be between £74mln and £80mln rather than the figure of at least £80mln expected by analysts.
Like-for-like sales in the 17 weeks to April 24 were down 2.7% and the group said it did not It not expect any improvement in underlying like-for-like trends in the short term. Finance chief Stephen Critoph, who has been with the company for 11 years, also stepped down.
The reports suggested another private equity group, TA Associates, is also mulling a offer for Restaurant.
Shares rose 2.6% to 326.4p.
Futura Medical (LON:FUM) added 11.11% to 17.50p as it said the recruitment phase has closed for its clinical study of MED2002, a topical gel for the treatment of erectile dysfunction.
Headline results are expected in the third quarter of 2016.
It came as small-cap pharmaceutical companies were healthier following the publication of a blueprint to tackle rising resistance to antibiotics.
Under the proposals drawn up by peer and economist Jim O’Neill, drug companies that don’t spend enough on developing new antibiotics would have to pay 0.25% of annual sales into a pooled fund to reward companies that do.
It would lead to the creation of a £1.4bn fund for early stage research and would result in payments to companies for every new antibiotic discovered.
The plan is designed to tackle the potential threat from superbugs, which it is feared will kill someone every three seconds by 2050 unless action is taken soon.