West Ham will face either Shakhtyor Soligorsk of Belarus or Slovenian side Domzale in the third round of Europa League qualifying.
The first leg is currently set to take place at the Olympic Stadium on July 28, with the second leg following a week later on August 4.
However, the Hammers have appealed to UEFA over switching the home and away legs around as the Olympic Stadium will be used for the London Anniversary Games on the weekend of July 22.
It usually takes seven days to convert the stadium from athletics mode to football mode and this therefore causes an issue for West Ham, who have held positive talks with both clubs over a switch.
"In order to give Stadium owners E20 Stadium LLP as much time as possible to prepare the arena for its first taste of European football, the club have today made official representation to request that the fixture be reversed," a West Ham statement read.
"If successful, Shakhtyor Soligorsk of Belarus or NK Domzale of Slovenia will visit Queen Elizabeth Olympic Park for the return leg on Thursday 4 August.
"Following post-draw discussions, both clubs have agreed to West Ham's request in principle and a final decision is expected to be ratified by UEFA in due course.
"Owing to the date of the Europa League fixture, the club has had to agree to work to a capacity of 54,000 for the Hammers' first two fixtures at London Stadium.
"And, given the proximity of the Anniversary Games to those opening two West Ham games, Stadium owners E20 Stadium PLP are doing their utmost to prepare the venue fully into football mode accordingly."
Slaven Bilic's side were knocked out at the same stage last season, losing 4-3 on aggregate to Astra Giurgiu of Romania.
Meanwhile, Aberdeen will face Maribor (Slovenia) or Levski Sofia (Bulgaria) if they overcome FK Ventspils in the second qualifying round.
The Dons claimed a 3-0 victory over their Latvian opponents at Pittodrie on Thursday evening and will be heavy favourites to go through next week.
Hibernian have been drawn against Bundesliga side Hertha Berlin, but must first overturn a 1-0 first leg deficit against Brondby.
The 2016 Scottish Cup winners were defeated at home to the Danish outfit, with Kamil Wilczek's first-minute strike enough to secure victory.
Hearts will play either Krasnodar (Russia) or Ventspils (Latvia) if they can overcome Birkirkara at Tynecastle on Thursday.
The Jambos were held to a goalless draw out in Malta, but will be confident of securing their passage through to the next round.
Europa League draw: Third qualifying round (first leg on July 28, second leg on August 4)
RoPS Rovaniemi /Lokomotiva Zagreb v Vorskla Poltava
Saint-Etienne v AEK Athens
Cliftonville/AEK Larnaca v Spartak Moskva
Pandurii Targu Jiu v Kairat Almaty/Maccabi Tel-Aviv
Vojvodina/Connah's Quay v Dinamo Minsk/St Patrick's Athletic
Partizan/Zaglebie Lubin v Strømsgodset/Sønderjyske
Austria Wien/Kukes v Shirak/Spartak Trnava
Hertha Berlin v Brøndby/Hibernian
West Ham United v Shakhtyor Soligorsk/Domzale
Luzern v Sassuolo
AIK Solna/Europa v Panathinaikos
İstanbul Basaksehir v Rijeka
Videoton/Cukaricki v Midtjylland/Vaduz
Levadia Tallinn/Slavia Praha v Rio Ave
Zimbru Chisinau (MDA)/Osmanlıspor* v Maccabi Haifa/Nomme Kalju
Heracles v Arouca
Piast Gliwice/IFK Göteborg v Beroe Stara Zagora/HJK Helsinki
Birkirkara/Hearts v Krasnodar
Aberdeen/Ventspils v Maribor/Levski Sofia
Debrecen/Torpedo-Belaz Zhodino v Rapid Wien
Admira Wacker Mödling/Käpäz v Slovan Liberec
AZ Alkmaar v Giannina /Odd
Lille v MTK Budapest/Qäbälä
Genk/Buducnost Podgorica v Häcken/ Cork City
Gent v Viitorul Constanta
Slovan Bratislava/ Jelgava v Omonia /Beitar Jerusalem
Oleksandriya v lasi/Hajduk Split
Neftci PFK/Shkëndija v Mladá Boleslav
KR Reykjavík /Grasshoppers v Apollon Limassol
*Participation subject to ongoing CAS proceedings.