Edinson Cavani will miss Manchester United's Champions League clash with Young Boys, Ole Gunnar Solskjaer confirming the striker suffered a slight strain in a friendly.
Cavani was not included as United went top of the Premier League in a 4-1 win over Newcastle United at Old Trafford on Saturday.
The Uruguay star has played only once this season and will not feature when United look to make a winning start to their European campaign in Switzerland.
Speaking at a media conference, Solskjaer told reporters: "Edi is hopefully back with us soon, he had a slight strain during the international break in a behind-closed-doors game. He's working hard to come back."
United, though, will have Cristiano Ronaldo at their disposal to potentially equal Iker Casillas' record of 177 Champions League appearances after he made it a second debut to remember against Newcastle following his move back to Old Trafford from Juventus.
The former Real Madrid star marked his return with a brace, his typically ruthless finishing looking like it will make United a force to be reckoned with after a transfer window in which they also added Raphael Varane and Jadon Sancho.
Asked about the quality he now has in his ranks, Solskjaer said: "This team has grown and matured over the last few seasons, that was always the plan.
"When I came in, we wanted a team with experience and quality who could challenge. David [de Gea] sat next to me, Harry [Maguire] has been here for a few years now, Raphael and Cristiano. We've learned."
Ronaldo's return and subsequent immediate impact has clearly increased the feel-good factor around United, with De Gea speaking to the influence he has had in a short space of time.
He said: "It's great to have Cristiano back home — the experience of Cristiano is amazing, he's a legend at the club already and it's great to have him back. It's massive for us."
United won each of their previous two Champions League clashes against Young Boys in the Champions League in 2018-19. Tuesday's opponents have won only one of their eight games against English opposition, but Solskjaer is not taking them lightly after Switzerland's shock win over France at Euro 2020.
"I was very impressed by the reaction in the game against France, when they were 3-1 down and you could see their quality when they turned that game around," said Solskjaer.
"I managed Molde against Basel and the game against Italy was impressive as well. Some of those players will be against us tomorrow."