Erik ten Hag blamed Manchester United's hectic schedule for Marcus Rashford's apparent groin injury that he sustained in their 2-0 Premier League win against Everton.
Rashford appeared to clutch his groin after he attempted to control a lofted pass from Christian Eriksen and he was forced off in the 81st minute.
The 25-year-old has not missed any of United's 29 Premier League games this season and has plundered 28 club goals this term. United's next highest scorer is Bruno Fernandes on 10.
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Rashford's injury did not appear to be linked to his withdrawal from the England squad last month when he sustained a knock in United's FA Cup quarter-final win over Fulham. The defeat of Everton was United's third fixture within a six-day period.
"I can't say in this moment, you are doctor, maybe?" Ten Hag said when asked for an update on the extent of the injury. "I am not. We have to wait, how bad or how good it is. Obviously he went off with a complaint, now we have to wait, set a diagnosis and we will see.
"Some things you can't avoid but it was avoidable. Why is the Premier League giving us the late Sunday night game (against Newcastle) and giving us the early Saturday game? I think it's not right.
"You run the risk, the players can't recover that quickly, we know all research that players need a certain period to recover and it accumulates. So then you run even more of a risk. It's also part of the schedule that we now find ourselves in this situation and now we can only pray he is not dropping off.
"Not any manager at this stage of the season will rotate so much. I know it's the toughest league of all the leagues we are in you need a squad to rotate to a certain point.
"But this was avoidable, it was not necessary to set the schedule like we have now. I think another fact is more important than the sporting element like protecting the players. Today we have seen a very entertaining afternoon but players can't do it so often when they're not fresh.
"We create a lot of chances but missing the chances is part of a lack of freshness in the final moment and the risk of injuries. We have to protect the players and it's in the interests of the total football. Everyone, the audience, wants to see great football and you need to have your best players.
"I had that consideration but in that moment, you want also Anthony Martial, just coming back, you want to bring them back into routines and togetherness. Because when they are together we have two goalscoring players, clinical players, who can finish games and that's what we need in the final stage of the season to be successful. That's the reason why we kept them on.
"Also, there was no indication, when there was an indication in the last days or this game, then of course I would have taken him off."
Martial came off the bench to claim his seventh goal of the season and only his first in the Premier League since December. Ten Hag is confident Martial can deputise lethally for Rashford if he is sidelined for a prolonged period.
"I'm not worried if Martial will not score," Ten Hag stressed. "You emphasise a lot in the Premier League, but West Ham United and Fulham in the FA Cup are also Premier League opponents, in the cup they are more front-footed and ambitious to win the games, it's often the pathway to quick success. So often those games are even more intense.
"Martial, when fit, he will contribute. No doubt, we've seen already when he's on the pitch, he makes a difference to the team, see Man City, see Liverpool. We have to keep him fit, he has to keep himself fit, then he will contribute, then he is a threat to the opponent and he can be clinical as well."
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