The Tennis Integrity Unit is assessing Alexandr Dolgopolov's defeat by Thiago Monteiro at the Winston-Salem Open as some bookmakers suspended their markets because of suspicious betting patterns.
Brazilian Monteiro beat Ukrainian world number 63 Dolgopolov 6-3 6-3 in the ATP Tour match on Sunday.
The odds shifted in favour of Monteiro, ranked 114, leading up to the match.
"The TIU was made aware of concerns over betting patterns during the match," it said.
"As with all match alerts, the TIU will assess, make a judgement and take appropriate action on the information received through its co-operative agreements with betting operators.