Police were called after a man carrying a baseball bat walked into McDonald’s in Oxford Road, Benson, at about 12.50am on Thursday last week and demanded the safe was opened.
A member of staff handed over an unspecified amount of cash before the thief demanded that a cash register was also emptied and the money given to him.
He then walked out of the restaurant and fled in the direction of Littleworth Road despite being pursued by a male member of staff.
Police said they were linking the robbery with one which took place at the restaurant the previous day but that the offenders were different people.
The second thief is described as white, about 6ft and slim. He was wearing a hooded top, biker jacket, black jogging trousers and training shoes and a dark face covering, possibly a balaclava. He was carrying a JD Sports drawstring bag.
Anyone with information should call police on 101.
• In August 2009, burglars stole more than £5,000 from the restaurant after cutting a hole in the safe and taking bags of notes and coins.