Fred Couples is wary of the United States' reliance on Jordan Spieth and Patrick Reed potentially backfiring on the final day of the Ryder Cup.

Spieth and Reed were paired together in each round of the foursomes and fourballs and have played a significant role in building USA's 9.5 - 6.5 lead over Europe going into Sunday's singles matches.

Having won one of their two contests with Henrik Stenson and Justin Rose on Friday, the pair defeated the same European duo in Saturday fourballs after halving their foursomes contest with Sergio Garcia and Rafael Cabrera Bello.

But Couples, who appeared in the Ryder Cup five times - winning in 1991 and 1993 - believes their heavy workload could have a negative impact.

"I think it's important to mix and match players well," Couples told Omnisport. "[The Europeans] do it well because they play their horses five times. If you look, Rory [McIlroy], Stenson, Rose and Garcia are going to play five matches.

"For us, we have the tendency not to wear out guys.

"We're riding Reed and Spieth like mad men; we're going to play them five times, but I think that's a lot of golf and I hope they're fresh.

"If they're not and they don't beat the guys they're playing [on Sunday], then it all backfires."

Brooks Koepka has won both of the matches he has been involved in, and Couples hailed the importance of players like the 26-year-old who appear to flourish under pressure. 

"The specialty of it is to find a guy like Brooks Koepka who is immune to all of this stuff," Couples said. 

"It doesn't mean he's going to handle the pressure perfectly, but I think this will make him a much better player, and that's what I like to look at."