Wesley Fofana joined Leicester last summer from Saint-Etienne for a reported £36.5mVillarreal forward Fer Nino has apologised for the tackle that left Leicester defender Wesley Fofana with a broken leg, saying: "At no time was it my intention to harm him."
Nino challenged French centre-back Fofana during a pre-season friendly between the sides on Wednesday.
Leicester manager Brendan Rodgers called it a "horrendous challenge".
He said Fofana, 20, needed another scan to determine how long he will be out for as the ankle was "so swollen".
"I am writing to publicly apologise, having already done so privately with him," Nino wrote on Instagram.
"At no time was it my intention to harm him, as unfortunately happened.
"I sincerely hope that he has a speedy recovery and can return to the pitch as soon as possible to continue showing that he is a footballer of the highest level."
Rodgers said Villarreal manager Unai Emery had apologised for the challenge "straight away".
"He's going to be a huge loss for us," said Rodgers, speaking in the build-up to Saturday's Community Shield against Manchester City.
"It was a horrendous challenge and we're obviously devastated for him.
"The medical team looked after him and the trauma doctor had to put his ankle back in place before went to hospital.
"The ankle was so swollen it was not safe to be looked at so he will have another scan, which should give a clear indication of how long he will be out."
As Jonny Evans is still to recover from the foot injury that forced him out of the FA Cup final win over Chelsea in May, Rodgers says he may now need to sign another central defender.
"It is something we will have to look at because we are definitely light in the central defensive area," he said.
"We have a small list of players to look at. There are people who are identified, so we will see."
'I believe Maddison will stay'
Maddison was signed from Norwich for an undisclosed fee believed to be about £20m in 2018The pattern in previous summers has been for Leicester to sell one of their big-name players.
With just over a week before the Foxes open their Premier League campaign against Wolves, the kind of transfer that saw Riyad Mahrez, Harry Maguire and Ben Chilwell leave in the past three years has failed to materialise.
There has been speculation around James Maddison, though, with Arsenal showing interest in the 24-year-old midfielder, who struggled with injury last season and missed out on a place in Gareth Southgate's Euro 2020 England squad.
Rodgers said: "I believe he will stay. There is clearly gossip and speculation at this time of year but James has been working very hard in training and is an important member of our squad.
"Hopefully this year can show the real top player that he is."
Rodgers also said Leicester had spoken to Belgium midfielder Youri Tielemans' representatives, and "he is happy".
