Liverpool's Kevin Stewart has had surgery on a hernia, a source has told ESPN FC.
The midfielder could well miss the Reds' remaining four matches of the season while he recovers.
Stewart, 23, has not featured for the Liverpool first team since January and had been appearing for the club's under-23s side to maintain fitness.
His future at Anfield is uncertain ahead of the summer, having failed to force his way into Jurgen Klopp's plans recently.
Sources said in January that Liverpool had rejected interest from several clubs during the transfer window, with Stewart valued at around £10 million.
Stewart signed a new long-term contract in November as a reward for his impressive performances in Klopp's team.
He moved to Liverpool in the summer of 2014 from Tottenham Hotspur and has made 20 appearances in total.
Meanwhile, youngsters Ovie Ejaria (ankle) and Sheyi Ojo (hamstring) returned from injury with an appearance for the U23s against Manchester City on Monday night.