Regarding the Islamic ruling of wearing  football shirts that have cross, Sheikh Ahmad Kutty, an Islamic scholar at the Islamic Institute of Toronto said:

“If the sign is clearly visible and highlighted, then it is not advisable to wear them; but if it not so, then, it may be permissible, especially if it has lost its religious connotations. The Prophet (peace and blessings be upon him) has discouraged Muslims from copying the specific religious symbols of people of other faiths; this is especially true of those that are associated with shirk or association of partners with Allah. Cross belongs to such symbols; therefore, it is not advisable to wear such shirts if these symbols are clearly visible…”