The Blues said Tuesday they were notified by the Football Association of an "adverse finding" in a urine sample provided by the 23-year-old Ukrainian winger.
Mudryk said in an Instagram post the results of his 'A' sample had come as a "complete shock" and insisted he had not intentionally taken a banned substance.
"We trust Misha," said Maresca on Wednesday.
"When this kind of thing happens you need to support your player in all aspects.
"Misha is a Chelsea player, it's my duty to be in contact with him. Me, the club, his team-mates, we are all there.
"Trust means we believe Misha."
Athletes are warned on the UK Anti-Doping (UKAD) website that they face a ban of four years if it is found a banned substance was taken intentionally.
If the violation involved a specified substance or a contaminated product, and the athlete can demonstrate they had no significant fault, ineligibility may range from two years to a reprimand, depending on the level of fault.
Mudryk has made 15 appearances for Chelsea this season and last played in a 2-0 win at German side Heidenheim in the Conference League on November 28, in which he scored his third goal of the season.
He has not featured in the past five matches in all competitions.
"I think he's going to come back, the only thing is we don't know when," said Maresca.
He added: "Any player in the world when this happens, they need support. No matter if he's 20 or 30, no matter if he’s English or Italian or Ukrainian. When this kind of things happens, we all need support. It's not about his age or his country.
"With Misha it is exactly the same. I'm there to try to help him in anything he needs because in this moment it's normal that he’s going need help from the club, from me, from his team-mates, and we are all there to try to support.”
Mudryk joined Chelsea for a reported £88.5 million ($112 million) from Ukrainian club Shakhtar Donetsk in January 2023.
Maresca's side are second in the Premier League and top the European Conference League table ahead of their match against Irish club Shamrock Rovers on Thursday.
© 2024 AFP