If you only play with 1 striker you will need to have a midfielder with very high mentality (maybe even higher than the st). Look at liverpool IRL. Gerrard has as many or even more offensive duties than torres. Also if you have too much difference between the mentality of the st and the midfielders, the st will be isolated. As TTF says, you should have a maximum of 8 noches between the most defensive player (CB or def mid) and the most offensive player (st, am). But of course the striker will be outnumbered as his is only 1 guys against 4 defenders, but support from midfielders will probably help