Toronto FC revealed on Friday that veteran defender Drew Moor was discovered to have an irregular heartbeat during a medical examination following a training session this week.

The club also said Moor will undergo further testing next week. As a precaution, Moor will not travel with the team for Saturday’s road game against the Columbus Crew.

Moor, 33, has played every minute of all five games this season, quarterbacking a three-man defence that has kept three clean sheets and conceded just four goals.

Last season, his first in Toronto after joining the club as a free agent, Moor played in 32 of 34 regular season games (all as a starter) and was a major reason why the Reds posted the second-best defensive record in MLS, with just 39 goals against – the year before, without Moor, Toronto gave up a league-high 58 goals.

Moor’s absence for Saturday’s game could mean another start for Chris Mavinga, who cracked the starting 11 for the first time in last week’s 2-2 draw at home against Atlanta United FC, although he was subbed out in the second half after a poor outing. Jason Hernandez, who recently signed as a free agent, could fill in and make his debut for TFC.

Another possible option would be to go with a four-man defence, featuring Eriq Zavaleta and Nick Hagglund (Moor’s regular defensive partners) in the middle, and dropping fullbacks Justin Morrow and Steven Beitashour into the back line.

TFC is undefeated through its first five games of the campaign, with one win and four draws. After the Columbus trip, the Reds return home for three consecutive home games at BMO Field vs. the Chicago Fire (April 21), Houston Dynamo (April 28) and Orlando City (May 3).