With Fernandes facing a three-match domestic ban, starting after Thursday's game against Porto in his homeland, the Reds will hope for good news on his fellow midfielders.
"I can't say in this moment," Ten Hag told MUTV's Liam Bradford after the game at Old Trafford. "I have to find out but, of course, when a player is coming off before half-time already, then there are some concerns.
"Also, I have seen how Mason came off. He was bleeding so it's clear there are some problems there and we have to see how they recover in the coming days."
United follow up the trip to Portugal in the Europa League in midweek with an away game at Aston Villa, before another pause due to the international break.