France captain Guy Forget believes the United States will be significantly weakened by the loss of Mardy Fish in their Davis Cup quarterfinal on Friday.

Both teams were rocked by withdrawals to key players this week.

The ninth-ranked Fish pulled out because of fatigue and was replaced by 66th-ranked Ryan Harrison. Meanwhile, Forget is without the 14th-ranked Gael Monfils, a former French Open semifinalist, because of an abdominal injury.

Harrison will be joined on the U.S. team by John Isner and doubles players Mike and Bob Bryan.

"I think these last-minute withdrawals are more harmful for them than for us," Forget said. "The American captain doesn't have a choice in singles. He can't choose one of the Bryan brothers. So Harrison will play on Friday.

"I thought Jim Courier might have called up Sam Querrey or even Andy Roddick. Harrison is a player for the future. We don't really know his true potential."

Courier, who won French Open titles in 1991-92, was tightlipped about why he chose the 19-year-old Harrison for the clay-court matchup at the Monte Carlo Country Club.

"A lot factors in the choice," Courier said. "Ryan was the best man for the job. That's why he's here."

Harrison faces a tall order against sixth-ranked Jo-Wilfried Tsonga.

"Obviously, Jo is a great player," Harrison said. "I'm just excited for the opportunity."

Forget said he picked Gilles Simon to replace Monfils because Richard Gasquet has an elbow injury.

France's victory in the doubles four years ago handed the top-ranked doubles pairing Bob and Mike Bryan only their second loss together in Davis Cup, and they have not lost since.

Only the Bryans, and Michael Llodra — who played alongside Arnaud Clement against the Bryans in 2008 — remain from those teams. The 31-year-old Llodra also played doubles in the 2002 semifinal, which France won 3-2.

"We've played Llodra for Grand Slam titles, we played him in the bronze medal match (at the 2008 Olympics)," Mike Bryan said. "We have probably played him at least 20 times. He's beaten us a bunch. We've beaten him a bunch."

Given that Simon is nursing a sore back and has little practice, Forget may pick Julien Benneteau, a French Open quarterfinalist in 2006, or Llodra for opening singles on Friday.

Harrison is not fazed about taking on the French on clay.

"Where I grew up in Louisiana I had 12 clay courts, and I grew up playing (on clay), so I'm very comfortable sliding," he said.

He'll be the lowest-ranked player to play a live singles match for the Americans since Fish — then ranked 74th — in the first round in Croatia in 2003.

The 11th-ranked Isner knows the pressure is on him, although he is trying not to think that way.

"Obviously, now I'm the No. 1," the 26-year-old said. "It doesn't change anything. I got to go out there on Friday and try to win a match for us."

The United States has won 32 Davis Cups, France nine. This is the 16th match between the nations dating back to 1905, with the U.S. leading 8-7 overall, and winning the last meeting 4-1 at home in the 2008 quarterfinals.

"France is a very deep team ... there are going to be five tough matches for us," Courier said. "We have to play our best to stand a chance. We did that with Switzerland. We'll be well prepared."

The winner plays Spain or Austria in the semifinals in September.