"He is someone that is going to have a big say from now until the end of the season," Martinez told the club's website (www.evertonfc.com).
"Even with Mo's experience internationally, his body is still adapting to the demands of the Premier League," the Spaniard added of a player capped 23 times by his country.
"He's picked up two soft-tissue injuries... it shows you that any player has to go through the process of adapting to the unique physicality of the Premier League."
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Everton, who are 11th in the Premier League table, travel to bottom side Aston Villa on Tuesday.
(Reporting by Shravanth Vijayakumar in Bengaluru; Editing by John O'Brien)
