April 9 (Reuters) - Manchester United ( MANU ) will have to carefully manage midfielder Kobbie Mainoo's return from a muscle injury after he participated in training ahead of Thursday's Europa League quarter-final at Olympique Lyonnais, manager Ruben Amorim said.

The 19-year-old England international has not played since United's FA Cup fourth-round home win against Leicester City on February 7, missing 10 games in all competitions since then.

His return was a welcome sight for United, who face French side Lyon at Parc Olympique Lyonnais in the Europa first leg and are also looking to improve their position in the Premier League, where they are 13th with seven matches remaining.

"He had some games out so we have to be careful with his fitness. We are really pleased with him but we have to be careful with him," Amorim told reporters on Wednesday when asked if Mainoo could start against Lyon.

"We are really happy to have more options and an option like Kobbie, with the quality that he has - he has played as a (number) six, as an eight and as a 10 - we are really pleased to have Kobbie but we have to be careful; we need Kobbie fit and fresh."

The Portuguese boss also backed the teenager to keep getting better as a player.

"When I see Kobbie, I see a lot of talent... I see some things that Kobbie has to improve: his pace in the game. He needs to improve in the build-up. Near the box, he has a lot of talent and that is why I think he did a really good game in the Europa League in that position," Amorim said.

"But I don't see a full player at the moment; he is 19. If I say I have seen the final player, I don't think I am helping Kobbie."

Dutch centre back Matthijs de Ligt, 25, will miss the game due to a foot problem.

Amorim said goalkeeper Andre Onana would start against Lyon.

Earlier on Wednesday, Lyon midfielder Nemanja Matic hit back at comments from Onana, describing the 29-year-old Cameroonian as "one of the worst goalkeepers" in United's history.

Onana had said "we are way better than them" when referring to Lyon this week and 36-year-old Serbian Matic, who spent five seasons at United, was annoyed by the remarks.

Amorim defended his keeper, saying: "If you see the full quote of Onana, it is quite different. The first sentence is that 'Lyon is a very, very good team'. Sometimes the players don't listen to the full quotes and it is just a misunderstanding. I know Matic also, he is a great guy, so tomorrow is going to be a normal game."