Matz, who was placed on the disabled list with a partial lat tear in July, allowed one hit and two walks on 78 pitches.
The Mets expect Matz to return from the DL in September as a starting pitcher only, but are being cautious dealing with the 24-year-old (Aug. 31).
In his four rehab outings, Matz has given up two runs and nine hits in 15 innings, striking out 13 batters. He threw six scoreless innings on 56 pitches on Aug. 26.
Matz was 2-0 with a 1.32 ERA in two major-league starts before going on the DL on July 10.