Sanchez explained to fulhamfc.com: "David is the Club's leading goal scorer at this moment in time. He's stepped up and scored the goals but we think he needs to be better physically so we're doing a lot of physical work to get him up to a level he needs to be at. The physical demands of this league, week in week out, are a big ask. It's a very physical league and players with the best attributes in the world, like Crespo and Shevchenko, have found it challenging.
"We can make David stronger with the weights and we'll improve his endurance. David has made a good start, three goals in the Premier League and that's from a limited number of starts. He's a great impact substitute but we want him to be a 90 minute player. He should have had two more goals from our games against Middlesbrough and Bolton and he's made two or three so I think he's done really well.
"His goal scoring rate for Northern Ireland, percentage wise, is better than Owen and Shearer's at international level, which for a small nation is phenomenal. He scored 13 goals in an international campaign - he's a class striker and he's proving that in the Premier League. I expect him to get ten goals this season without a doubt and a lot of Premier League strikers would be happy with that.
"He played with a big striker alongside him for Northern Ireland and since the loss of Brian McBride we haven't had that type of striker alongside him. He's been asked to do roles that aren't his strengths. David's a box player and in the area that aren't too many finishers of his quality in the Premier League."