- Liverpool ratings: Jota 8/10 for scoring club's 10,000th goal
The Brazil international had transitioned from his defensive midfielder role to centre-back to fill in for the injured Virgil van Dijk, but a knock in the 30th minute further depleted Jurgen Klopp's ranks.
"It is exactly the last thing we needed," said Klopp, when asked after the match about the seriousness of the injury.
"I know [Fabinho] felt a hamstring, and that's not good. He said he could have played on but no sprints, which doesn't help. We will see, we will know more after a scan but clearly it isn't good," he added.
Fabinho had been filling in for Van Dijk in the centre of defence since the Dutchman suffered a serious knee injury in the Merseyside derby against Everton. Reds defender Joel Matip has also been battling injuries and did not dress for Tuesday's match.
"Rhys Williams he's only 19-years old and I think he's played more Champions League games than Premier League games -- that's rare. We're doing really well but its a shock for a team because now we have to sort that injury," added Klopp.
Diogo Jota gave Liverpool the lead with his close-range shot in the 55th minute off Trent Alexander-Arnold's cross. The Portugal man's goal was the 10,000th across all competitions in Liverpool's illustrious history, 128 years after Jock Smith scored their first in the Lancashire League.
Defending Danish league champions Midtjylland, playing their first-ever road Champions League match, held their own against a rotated Liverpool side that saw Sadio Mane, Mohamed Salah, and Roberto Firmino make second-half appearances.
Midtjylland made portions of the match lively with a couple of good attempts from Anders Dreyer, had the best chance of the game late when he juked into space in the Liverpool box but, with Alisson to beat, he could only find the side-netting.
Liverpool sealed the three points after Salah drew a foul in the box in the stoppage time, converting the penalty for Liverpool's second goal on the night.
Despite their steady form amid the mounting injuries, Klopp accepted that the Premier League champions were in a difficult period.
"It was a tough night. It's a bit like in a marriage, there are good and bad times. It's not a bad time but it's a tricky time. 100% we have to stick together and fight harder and that's what the boys did tonight," he said.