McLean has been pitching in long relief out of the bullpen his last two games. He’s been piggy-backing off Montas, but has been coming in mid-inning — which is unusual. Typically, teams will bring in an experienced reliever to end the inning to give the second “starter” a clean inning and a more normal warmup.
Figure Montas has at least 2 more starts and then Manaea will need his share. It’s possible they keep using McLean like that and then call him up as a long reliever/spot starter to get him in the big leagues sooner.