Both goalkeepers have started four of United's eight knockout fixtures in the Europa League, but Dean Henderson has emerged as No. 1 in the Premier League recently, with David De Gea relegated to Cup duty.
"I think there's loads of difficult calls to make, the whole squad has contributed so much," said Solskjaer ahead of their final against Villarreal.
"It's probably a different scenario with the keepers than it's normally been because they've shared I don't know how many games, close to 60 and both of them are in and around the 30 mark and both have done really well so it will be a difficult call of course. But I will have to make two or three other difficult calls as well."