Kyle Edmund suffered a first-round defeat at the Qatar Open in Doha on Monday as Filip Krajinovic came from a set down to advance at the Brit's expense.
No. 6 seed Krajinovic secured the win 4-6, 6-3, 6-3 after two hours and 17 minutes on court.
Elsewhere at the tournament, seventh seed Adrian Mannarino was upset 6-3, 6-4 by Alexander Bublik of Kazakhstan, and Spain's Fernando Verdasco saw off compatriot Pablo Andujar 6-4, 6-3.
Meanwhile, France's Jeremy Chardy defeated Gregoire Barrere 6-3, 3-6, 6-3 in a back-and-forth contest, and Aljaz Bedene of Slovenia overcame Mikael Ymer 3-6, 6-4, 6-3.
American Tennys Sandgren was eliminated by Corentin Moutet 7-6(3), 6-4, while Miomir Kecmanovic of Serbia defeated Australian Jordan Thompson 6-4, 6-2.