Lentjes suffered a broken leg in the side’s 28-22 loss to the Rebels at Forsyth Barr Stadium and his season appears to be over.
The Highlanders will miss Lentjes, as the newly appointed skipper had impressed in the opening four games.
But there is an able substitute in Dillon Hunt and McDowall will be itching to get a crack at this level.
The former New Zealand schools player had a mighty impressive campaign for Otago in the Mitre 10 Cup last season and was desperately unlucky to not be picked up by any Super Rugby sides.
McDowall turns 22 next Sunday and it would be a great birthday present for him to play his first game for the Highlanders. He has been training with the squad.
The Highlanders left for South Africa yesterday from Dunedin, heading to Sydney first, and will arrive in South Africa some time today.
A decision on who takes over from Lentjes as captain will come over the next couple of days. Halfback Aaron Smith appears the obvious candidate, although he has plenty on his plate already and perhaps does not need the added burden of captaincy.
Liam Coltman is also another prospect but he was believed to be reluctant to be involved in the captaincy.
The co-captaincy route is one the side has used in the past and it may be the option to pursue.
It is a long plane ride to South Africa and the team will have plenty of time to ponder what happened against the Rebels last Friday night.
The team made too many errors and coughed up plenty of ball just at the wrong time, lacking composure when the pressure came on.
The side has lost a truckload of experience this year and it was always going to take time for the team to get combinations going and get cohesion between the players.
Super Rugby, though, is a unforgiving arena and players have been exposed for poor decision-making and struggling to perform skills under pressure.
The side will play the Bulls in Pretoria on Sunday before heading to Argentina to take on the Jaguares in Buenos Aires on March 15.
The Highlanders have slipped to 13th in the standings but the Bulls are even worse and sit bottom of the table. The Bulls side is similar to the Highlanders, having lost a ton of talent from last year, and struggling to get any combinations going. The team is yet to win a game.
In other results, the Waratahs picked up their their win of the season, beating the Lions in Sydney on Friday night, 29-17. The Hurricanes thrashed the Sunwolves in Napier while the Sharks beat the Reds 33-23 in Brisbane. The Jaguares were too good for the Bulls, winning 39-24 in Pretoria.