Mannella is one of seven players from Toronto FC's senior squad lent to TFC 2 for the road game against the Charleston Battery. The others are goalkeepers Quillan Roberts and Alex Bono, defender Ashtone Morgan, midfielders Manuel Aparicio and Jay Chapman, and forward Jordan Hamilton.
All seven are between 19 and 21, with the exception of the 24-year-old Morgan.
With first-teamer Justin Morrow facing a suspension pending an appeal of his red card in Columbus last weekend, Morgan is getting the run-out with TFC 2 to get some more game experience.
Mannella, 20, signed with Toronto FC last September, becoming the 10th player in club history to graduate to the first team from the academy. He has not played for the first team yet but made the bench last October against the New England Revolution.
Mannella and Roberts have both been called up to the Canada squad for friendlies later this month against Guatemala and Puerto Rico.
Saturday's game makes the start of the season for the 24-team USL pro circuit.
FC Montreal opens play March 28 against visiting Toronto. The next day, the Vancouver Whitecaps 2 visit the Seattle Sounders 2.
MLS teams are looking to the third-tier USL Pro league this season as a way to bridge the gap between their academies and the first team.
Toronto, for example, signed an initial batch of eight players to USL contracts and will augment the TFC 2 roster each week with players from the senior academy team and the Toronto FC roster.
The seven loans announced Friday could last one week or the entire season. Some will likely remain with the USL Pro side the whole season while a few will bounce up and down.
"It's basically juggle three pods or groups and bring them together and hopefully mesh on a Saturday," said TFC 2 coach Jason Bent, a former first-team assistant coach and academy head.
TFC 2 announced another four USL signings Friday: defender Daniel Fabrizi and midfielders Massimo Mirabelli, Adam Bouchard and Mark Serjeant.
Fabrizi, 23, helped York University win the CIS championship last year while Mirabelli, 23, spent the past two seasons with FC Edmonton of the NASL.
Bouchard, 19, originally joined the TFC Academy last October after spending time in Uruguay with Defensor Sporting Club's youth system. Serjeant, 19, played last season at Grand Canyon University in Phoenix.
An 18-man playing squad is flying south to Myrtle Beach and then will travel by bus to Charleston. Bent will be assisted by academy senior team head coach Stuart Neely.
"There's some talent in the team for sure," said Bent. "Their character is coming out more and more with each training session."
Bent will play either Bono or Roberts in goal the whole game, barring something untoward.
Defender Skylar Thomas and forward Edwin Rivas are injured and will not play. Mexican forward Sal Bernal is still working on visa issues.
The Battery, which is affiliated with the Houston Dynamo, had an extensive pre-season. They went 7-1-2 in exhibition play, including a 4-1-1 mark against MLS and NASL teams, and they ended their run with four wins in seven days against the Jacksonville Armada, Old Dominion University, Clemson University and the Carolina Railhawks.
"They're a team that's made the playoffs consistently over the years ... we're expecting a pretty good game for our first test," said Bent.
TFC 2 won't play its home opener until May 23 against the Rochester Rhinos. The first two home games will be at BMO Field until its new facility at the Ontario Soccer Centre in suburban Vaughan is complete.
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