No 1 Tim Krul and Rob Elliot are still recovering from their long-term knee injuries.
And United manager Rafa Benitez must choose between Darlow and summer signing Matz Sels at Craven Cottage on August 5.
Darlow was outstanding in the latter part of last season after Elliot, like Krul before him, ruptured his anterior cruciate ligament.
The 25-year-old has experience of the Championship from his time at Nottingham Forest, and he gave Benitez a timely reminder of his ability ahead of the Fulham game in Tuesday night’s win over Southend United.
Matz is good competition,” said Darlow. “We’ve got some very good goalkeepers now. It’s going to be a fight all season for who’s going to be playing.
“I knew I needed to play,” said Darlow.
“It’ll stand my in good stead, hopefully, for Saturday against Vitesse.
“Then we’ll see what happens going into the season.”
“It’s been good for me. I’ve come back and been very good.
“I’ve worked hard, and I’ll keep working hard with Simon (Smith, United’s goalkeeping coach).”