Chelsea midfielder Billy Gilmour will be out for up to four months after undergoing knee surgery, head coach Frank Lampard has confirmed.

The 19-year-old was hurt after a collision with Luka Milivojevic during the Blues' 3-2 Premier League win over Crystal Palace on Tuesday.

"Billy Gilmour's had an operation on his knee this morning, unfortunately, so he'll be out, we estimate, for somewhere between three and four months," Lampard said on Friday.

Gilmour had been flourishing this season under Lampard, making 11 appearances in all competitions, and had recently moved above Italy international Jorginho in the pecking order at Stamford Bridge.

Lampard says there is a stroke of fortune about the timing of the injury, with much of Gilmour's recovery likely to be taking place during the off-season between this term and the start of 2020-21, but he accepts the news was a blow to the player.

"I'm obviously very disappointed, we all are and Billy is himself," Lampard said. "I spoke with him yesterday [Thursday] at length and just gave him support, really.

"He's a tough boy. It hit him hard – I get that as well, particularly as a younger player who's just made his breakthrough in recent times and was doing so well – but it's part of football and I tried to explain he can be very pleased with the impact he's had this season. Part of our job as players is to get on with these things and learn our lesson quickly and his attitude will get him back as quick as he possibly can.

"His character is fantastic. Particularly with his age, the personality he has shown in getting in and around the first-team squad, getting himself into the team, I'm very sure he'll show the same character and do everything right with the rehab and tackle it.

"He's got a close-knit family around him who'll be there for him and we're his family too, we'll be there for him and the small bonus is it will hopefully cover a period that's off-season and pre-season, so he's maybe not missing as many games as he might have done."

Chelsea, who sit third in the Premier League table with four matches remaining, face Sheffield United at Bramall Lane on Saturday.