While Lavia was already expected to miss out on Thursday's London derby with Tottenham Hotspur, Fofana was a surprise omission from the squad.
The France international had only recently returned from a long-term hamstring injury and started the game at Arsenal before the March international break.
Although Chelsea were able to run out 1-0 victors over one of their fierce rivals in their absence, Maresca and the Blues could naturally benefit from having the pair available for selection.
Maresca speaks on Fofana, Lavia
Speaking at a press conference on Thursday night, Maresca gave an update on the pair, indicating that there is currently no specific timeframe for their respective returns.
As quoted by football.london, the Italian said on Fofana: "A muscle problem a few days ago and we are waiting for some more checks."
He added: "We don't know yet. We are waiting for both. Romeo looks a little bit better injury compared to Wes, in terms of probably Romeo can be back earlier than Wes."
While Chelsea face a hectic run of fixtures due to the Conference League quarter-final with Legia Warsaw, neither Fofana or Lavia have been included in the European squad due to their fitness battles.
As well as Fofana missing the entirety of 2023-24 with a serious knee injury, Lavia only made one substitute appearance at the end of December.
Is Maresca concerned about Lavia?
Although Lavia has made nine starts and four substitute outings this campaign, he has been sidelined with injury on several occasions.
Nevertheless, Maresca is not too downbeat on the situation, saying: "If you compare Romeo's games this season to last season, he's already improved. Because this season it was difficult to go the other way.
"But the target with Romeo is just to try to keep him fit as much as we can. The next year he'll play more games than this season."
Fofana and Lavia now have 10 days to try to recover for the Premier League fixture with Ipswich Town on April 13, it seemingly apparent that only Lavia may have a chance of returning to the squad.
Written by
Darren Plant