Marcos will turn his attention to the North American summer hard court season after falling in his Newport opener on Tuesday.
Marcos suffered a tight 7-6(5), 6-3 defeat to longtime friend and rival Gilles Muller at the Dell Technologies Hall of Fame Open. It was just his second loss to Muller in five head-to-head meetings.
Despite firing nine aces and claiming 24 of 30 points on his first serve, Marcos fell to Muller after one hour and 24 minutes. He earned one break from four opportunities.
Marcos also fell in his doubles opener with Mischa Zverev, as fourth seeds Marcelo Arevalo and Miguel Angel Reyes Varela prevailed 7-6(2), 6-4.
Marcos will look to a change in surface to turn around his fortunes, as he shifts to the hard courts. He will compete at ATP World Tour stops in Atlanta, Toronto, Cincinnati and Winston-Salem, followed by the final Grand Slam of the year at the US Open.