The Everton full-back sustained an ankle injury in April's Merseyside Derby against Liverpool, ruling him out of the final four matches of the Premier League season.
After being included in Ukraine's Euro 2024 squad, Mykolenko was forced to miss his country's first warm-up game against tournament hosts Germany.
However, he returned to action in Friday's 3-1 defeat against Poland, getting 45 minutes under his belt before being withdrawn at half time.
Rebrov provides update on Mykolenko injury
Mykolenko was presented with another starting opportunity in Tuesday's meeting with Moldova in a bid to build up his match fitness ahead of 2024.
However, his evening was ultimately cut short in the 30th minute when he was forced off due to a suspected ankle injury.
While there will be concern surrounding Mykolenko's fitness, Rebrov is hopeful that the 25-year-old has avoided serious injury ahead of the European Championships.
"Mykolenko has had an MRI scan already and will have another scan tomorrow [Wednesday]," Rebrov told reporters following the 4-0 win over Moldova. "We will see what happens, but I feel a lot calmer now from the initial incident."
How important is Mykolenko to Ukraine?
Having represented his country on 41 occasions, Mykolenko is regarded as one of the senior members of Rebrov's 26-man squad.
A fully fit Mykolenko would likely start as Ukraine's left-back, allowing Arsenal's Zinchenko to operate in the middle of the park.
However, Zinchenko will have to drop into the left side of defence if Mykolenko is unavailable for any of Ukraine's three group matches.
The Everton man faces a race against time to prove his fitness ahead of Ukraine's tournament opener against Romania on Monday.
The Blue and Yellow will then face Belgium on matchday two, before they wrap up the group stage with a game against Slovakia.