Syndergaard appeared in three games for the Mets this spring, allowing five runs on five hits in 8 2/3 innings, posting a 5.19 ERA. He struck out 10, but also walked five.
The 21-year-old right-hander was acquired by the Mets last offseason in the trade that also brought back catcher Travis d'Arnaud from the Toronto Blue Jays in exchange for Cy Young winner R.A. Dickey.
Last season for the Mets' Single-A and Double-A affiliates, Syndergaard went a combined 9-4 with a 3.06 ERA, striking out 133 and walking only 28 in 117 2/3 innings over 23 starts.
The Mets also reassigned fellow pitching prospect Rafael Montero to minor league camp on Tuesday.
Montero appeared in five games, posting a 3.00 ERA over nine innings of work. He allowed six hits, struck out five and walked two. The right-hander went a combined 12-7 with a 2.78 ERA between Double-A and Triple-A last season. He struck out 150 and walked 35 over 155 1/3 innings.