Former world number one Andy Murray lost in straight sets to France’s Richard Gasquet in his first singles match since career-saving hip surgery in January as action began at the Cincinnati Masters.
Following his 6-4, 6-4 defeat at the Lindner Family Tennis Center, the Scot announced that despite not feeling any major pain, he will not play singles at the US Open later this month.
He had been asked to make a decision on accepting a wildcard for the upcoming Grand Slam prior to facing Gasquet.
"We were hoping to maybe hold a wildcard until a little bit closer to the time to see how I feel and get some matches hopefully and a bit of practice," Murray said.
"[It was] a decision I made with my team.
"I didn't want to take a wildcard today because I just didn't know how I was going to feel after a match.
"I felt like I wanted to be fair, for me to maybe try and get a couple of matches in before making a decision like that."
Murray could potentially enter the singles at next week's Winston-Salem Open, but plans to play men’s doubles and mixed doubles at the US Open, which starts on August 26.
The three-time Grand Slam champion broke down in tears at January's Australian Open, dreading his career might be over.
He felt surgery on his long-standing hip injury could end his chances of playing singles.
But it has instead left him pain-free and allowed him to resume his career.
Gasquet will play fourth seed Dominic Thiem of Austria in the second round of the Cincinnati Masters, an Association of Tennis Professionals World Tour Masters 1000 event.
American John Isner, the 13th seed, also progressed, defeating Serbia's Dušan Lajović 7-6, 1-6, 7-5.
But 14th seed, Croatian Marin Čilić, fell to a 4-6, 6-7 defeat at the hands of Moldova's Radu Albot.
In the Women's Tennis Association Premier 5 event, 11th seed Latvian Anastasija Sevastova was the most notable casualty, defeated 6-7, 7-6, 4-6 by Russia's Svetlana Kuznetsova.
British number one Johanna Konta was beaten 3-6, 6-3, 5-7 by Swedish qualifier Rebecca Peterson.
Seven-time Grand Slam singles champion Venus Williams ended a four-match losing streak by overcoming fellow American Lauren Davis 7-5, 6-2, while Russia's Maria Sharapova beat fellow wildcard Alison Riske 6-3, 7-6.
It sets up a mouthwatering clash with top seed Ashleigh Barty of Australia in the second round.
Barty defeated Sharapova in the fourth round of this year's Australian Open.
Another player to advance was ninth seed Aryna Sabalenka of Belarus, thanks to a 6-1, 6-4 win over Croatia's Petra Martić.
However, Danish former world number one Caroline Wozniacki was humbled by Ukrainian teenager Dayana Yastremska in straight sets, 4-6, 4-6.