Fuller began his career at Jamaican side Tivoli Gardens

Fuller was set to join Pompey for �2m a month ago but failed a medical due to a long-standing knee problem.

"The on/off deal to sign Fuller has got the green light on a pay-as-you-play basis," said a Portsmouth statement.

The 24-year-old joined Preston from Hearts two years ago and scored 31 goals in 63 games.

Pompey chief executive Peter Storrie added: "It was one of the hardest things I had to do a month ago when I told Ricardo the medical diagnosis.

"I have been going hammer and tongs at this deal until past midnight and, along with the backroom staff today, have worked hard to pull this off.

"Originally as a club we just could not take the gamble on paying out a lot of money given the advice we were given.

"We then watched him against Watford and have now concluded a deal that is sensible for all concerned.

"It gives Ricardo his deserved chance to fulfil his Premiership ambitions and at the same time insuring us against further damage to his knee.

"There are no doubts about Ricardo's ability as a footballer and a striker and we are delighted to now have him on board to bolster our striking options."