The unconventional filled skutterudite superconductor, PrPt4Ge12(Tc ~ 7.9 K), was recently discovered, for which zero field muon spin relaxation (ZF-MuSR) experiments reveal that timereversal symmetry (TRS) breaking occurs below Tc. The origin of the TRS breaking is not clear. ZF-MuSR experiments in the (Pr,Ce)Pt4Ge12 alloy series reveal that Pr-Pr intersite interactions are important for the broken TRS, but pair-breaking by Cedoping suppresses superconductivity. To shed more light on the TRS breaking superconductivity in PrPt4Ge12, it would be inportant to perform a non-pair-breaking doping study. We propose to use ZF-MuSR to investigate how the TRS-breaking superconductivity of PrPt4Ge12 evolves with La substitution, while Tc of the end compounds PrPt4Ge12 and LaPt4Ge12 are very close.