Liverpool's 5-1 Champions League victory over Eintracht Frankfurt ended their four-match losing streak but came at a cost as Alexander Isak and Jeremie Frimpong suffered injuries.
British record signing Isak was taken off at half-time with a groin problem while right-back Jeremie Frimpong's stop-start to the campaign continued after he was ruled out for a "few weeks" with a hamstring injury.
Head coach Arne Slot is hoping his £125 million (€143.8m) striker - who started alongside fellow number nine Hugo Ekitike for the first time - is not too badly affected as only last week he vowed the Sweden international could now be judged fairly after missing pre-season.
"Let's hope it's not that bad, but he had to go off because he felt his groin," said the Reds boss.
"Many people wanted me to play him more and we had to find the balance and unfortunately today that balance didn't work out for us perfectly. But let's hope for the best.
"Today with Alex and Hugo, I brought two players on the pitch who are usually able to score goals.
"Alex was a few times close but had to go off at half-time, and that's the difficult balance we are having with him.
"When he came to the club, he had hardly trained. So you bring him step by step forward, and then you feel there must be a moment where he can play twice a week, and the first time we try - he did it with Sweden as well - he has to go off.
"Normally you try to prepare players for once a week football, but if you are Liverpool you play every three days or normally three times in eight days but we've been unfortunate this season we have to play three times in seven days.
"We've tried to prepare him for that, we were really careful, and he was perfectly fit when he came back from the national team (last week) before the United game.
"We thought he was well prepared for that but the margins at the top are small. I'm hoping it won't be that bad, because if he's out for a few weeks it will put him back. So let's wait."
While Isak failed to add to his solitary goal so far Ekitike, on his return to the club he left in the summer, sparked the comeback from 1-0 down with the equaliser, which was followed by set-piece headers from centre-backs Virgil van Dijk and Ibrahima Konate before half-time.
After the break Florian Wirtz, the £100m (€115m) summer signing from Bayer Leverkusen, started to find his feet and provided assists for Cody Gakpo and Dominik Szoboszlai.
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