Pictures of the underside of Sergio Perez's (33) car swiftly circulated around rivals after the Mexican crashed in Monaco Grand Prix qualifying and marshalls removed the car with the help of a crane.
Stella, a former Ferrari race engineer, told reporters at the Spanish Grand Prix he had been impressed by what he had seen.
"Personally I spent some time (looking) but the 100 aerodynamicists at McLaren will be spending a little bit more time," said the Italian.
"It's very interesting indeed and also shows the complexity and the quality of their development. To be honest, when I saw it, I said 'Hats off to Red Bull'. I can understand why they have this kind of performance."
Red Bull have won all six races so far this season by a comfortable margin, with double world champion Max Verstappen (25) taking four victories and Mexican Sergio Perez the other two.
Verstappen acknowledged on Thursday that Red Bull could win every race.
McLaren announced earlier in the week the signing of Red Bull's chief engineering officer Rob Marshall (55) in something of a coup for the former champions as they restructure and chase a return to the top.
Marshall has spent 17 years at Red Bull, working with top designer Adrian Newey (64) and involved in Red Bull's championship domination from 2010-13 with Sebastian Vettel (35). He joins in January as technical director, engineering and design.
"Rob will join the team with a unique level of experience, know-how in terms of engineering and design of Formula One cars. He has also been instrumental in creating such a strong technical department at Red Bull," said Stella.
"I think the technical structure is well set now and quite strong," he added, when asked about further signings.
Verstappen wished Marshall well.
"Honestly when I heard the bid that he got, I understand why he left. It's fine. He did an amazing stint at Red Bull, I think everyone's very thankful for what he did for our team," the Dutch driver said on Thursday.
"Hopefully he has a good time where he's going and a bit more cash in the bank doesn't hurt."
