British sprinter Chijindu Ujah finished sixth in the 100m in his Diamond League debut in Paris on Saturday.
Ujah, 20, is battling with James Dasaolu for the third sprint place in the British team for August's European Championships in Zurich.
However, Ujah, who clocked 9.96 seconds last month, could only run 10.20secs, as Michael Rodgers claimed victory.
The American finished ahead of Trinidad's Richard Thompson and Kim Collins from Saint Kitts and Nevis.
Dwain Chambers and former world junior champion Harry Aikines-Aryeetey are guaranteed their places for the European Championships by finishing first and second at last month's British trials.
Ujah came third in that race but his place in Switzerland is not certain, especially after Dasolu, who missed the trials through injury, ran 10.03secs at a meeting in Lausanne on Thursday.
Elsewhere in Paris, Laura Muir and Laura Weightman both ran personal bests in the 1500m.
Muir set a new Scottish record and became the fifth fastest Briton ever over the distance as she clocked 4.00.07 to finish sixth in a race won by Holland's Sifan Hassan in a world-leading 3:57.00. Weightman was eighth in 4:00.17 to go sixth on the British all-time list.
GB's Shara Proctor missed out on a top-three finish in the women's long jump. The 25-year-old, the defending overall Diamond League champion, was fourth with a leap of 6.70m, well short of the 6.92m jump of France's Eloyse Lesueur.
GB's Tiffany Porter was fifth in the women's 100m hurdles in 12.72secs, while European number one Niall Flannery could only finish seventh in the men's 400m hurdles.
British champion Eilish McColgan finished last in a women's 3,000m steeplechase won by Ethiopia's Hiwot Ayalew.
Britain's David Weir, who won six gold medals at the 2008 and 2012 Paralympic Games, won the men's 1,500m wheelchair race in 3:18.78.
The 2008 Olympic 1,500m gold medal winner Asbel Kiprop dropped down to 800m and clocked 1:43.34, the fastest 800m time in 2014.
Jamaican sprint star Shelly-Ann Fraser-Pryce finished fifth in the women's 200m as she continues to recover from a leg injury. Nigeria's Blessing Okagbare took gold in 22.32 with American Allyson Felix second in 22.34.
Sanya Richards-Ross from the United States won the women's 400m in 50.10.