Toronto FC announced on Friday that a cardiac arrhythmia was discovered in center back Drew Moor during a medical examination following a training session earlier this week.

According to TFC, further testing will take place next week to determine Moor’s exact diagnosis and treatment plan. As a precaution, he will not travel to Columbus for Toronto’s match on Saturday at Crew SC (8 pm ET | TSN; MLS LIVE in the US).

Moor, 33, signed with Toronto last offseason as a free agent. The veteran defender played a huge role in the defensive turnaround that led to TFC’s club-best regular season and MLS Cup appearance in 2016, starting 32 regular-season matches as the Reds finished tied for the second in the league in goals allowed.

He had started all five of Toronto’s matches entering this weekend. Offseason signing Chris Mavinga would be a natural candidate to replace him in the starting lineup if TFC stick with their 3-5-2 formation.