Martinez told reporters: "The big negative is Deulofeu. He has pulled his hamstring. We don't know how bad the tear is. It could be a long time.
"I was very pleased with performance at the end. It wasn't one of our best days. We didn't move the ball well.
"What we did when it got to 1-1 was change the mindset. We were adventurous and brave. The 4-1 scoreline flattered us."
The win moves Everton inside the top four in the Premier League.