Top quark mass determination and [Formula Presented] correction to the toponium [Formula Presented] energy level

Recently the full [Formula Presented] correction to the heavy quarkonium [Formula Presented] energy level has been computed (except the [Formula Presented] term in the QCD potential). We point out that the full correction (including the [Formula Presented] term) is approximated well by the large-[Formula Presented] approximation. Based on the assumption that this feature holds up to higher orders, we discuss why the top quark pole mass cannot be determined to better than [Formula Presented] accuracy at a future [Formula Presented] collider, while the modified minimal-subtraction [Formula Presented] mass can be determined to about 40 MeV accuracy (provided the 4-loop [Formula Presented]-pole mass relation will be computed in due time).