As reported by Goal, Kovacic is in talks with the Blues over a loan move to Stamford Bridge, with the Croatia international having grown frustrated at his lack of regular first-team football at Madrid.
Kovacic, who appeared five times at the World Cup as Croatia reached the final, has often had to play second fiddle at Santiago Bernabeu, with the likes of Casemiro, Luka Modric and Toni Kroos preferred in central midfield.
And when asked about the player's impending switch to Chelsea, Lopetegui confirmed that, should he leave, Madrid will try to bring in a suitable replacement before the transfer window closes.
"There's nothing 100 per cent certain yet," he told a press conference.
"Mateo has said he wants to leave. I want him to stay – he's an important player. We'll see how everything ends up. If he happens to leave, we'll look for solutions."
Pressed on how he would react if Kovacic does depart, Lopetegui added: "The solutions are something we'd speak about privately within the club. If Mateo does leave, a player of his level, which is extremely high, we'll have to look for someone at that type of level.
"To reach all of our objectives we need to have a balanced team and he [plays] a very important position and he's a very important player."
The Madrid boss reiterated the message given by club president Florentino Perez, however, who had joked that the Croatian can leave if a club pays his mammoth €750 million (£670m/$870m) release clause.
"As for Modric, it's the same as I've said - Perez spoke in a completely clear manner and there's no reason for me to add anything else."
Madrid are currently in talks over the signing of Thibaut Courtois from Chelsea, with the goalkeeper having been absent from training as he looks to force through a move to the Spanish capital.