By Caroline Cheese BBC Sport at Wimbledon

Andy Roddick v Roger Federer

RODDICK (5) v FEDERER (4) 20------------Age-----------21 American----Nat--------Swiss 0------------Slams-----------0 7--------Career titles-------8 $2.5m----Earnings----$4.7m 0------Head-to-head-------3

Both Roddick and Federer have long been touted as potential Grand Slam winners and now they meet in a potentially explosive semi-final.

World number four Federer is in his first ever Grand Slam semi, Roddick his second after reaching the last four at the Australian Open earlier this year.

But it is Federer who has the edge in previous matches between the pair.

The 21-year-old Swiss player has won each of their three meetings, all on hard courts, and has lost only one set in the process.

But Roddick, seemingly a changed man after the introduction of new coach Brad Gilbert, has been highly impressive on grass this season, winning at Queen's and dropping only one set so far at Wimbledon.

Roddick ready for Federer

Federer, who has also conceded just one set, is still troubled by a back injury that developed in his fourth round match, and concerns over his fitness will grow if the match becomes a five-set battle.

Mark Philippoussis v Sebastien Grosjean

PHILIPPOUSSIS v GROSJEAN (13) 26------------Age-----------25 Australian----Nat-------French 0------------Slams-----------0 9--------Career titles-------3 $5.6m----Earnings----$5.0m 2------Head-to-head-------2

Philippoussis and Grosjean's encounter is set to be an intriguing clash of styles.

While the unseeded Australian, a natural grasscourt performer, has banged down 153 aces in reaching the semis, Grosjean's return of serve has been equally impressive, as Tim Henman would attest.

Both are in the Wimbledon semi-finals for the first time, but both have experience of the last four stage at other Grand Slams.

Grosjean reached the Australian Open semi-finals in 1999 and 2001, the year in which he lost a two-set lead and had two match points against compatriot Arnaud Clement.

Philippoussis, who has battled back to fitness after a career-threatening knee injury, made the 1998 US Open final, losing to fellow Australian Pat Rafter.