The All Blacks head to South Africa this week for their Tri-Nations opener without their four first choice second-rowers.
Chris Jack and Ali Williams miss the Durban test through paternity leave and a broken jaw, respectively, while James Ryan and Jason Eaton have been ruled out for the season with knee injuries.
And with Springboks pair Victor Matfield and Bakkies Botha ruling the Super 14 roost this season, the paucity of expert line-out jumpers is a concern.
However, Donnelly produced a confident performance in the Junior All Blacks' 50-0 whitewash of Australia A at Carisbrook.
And Cooper told The Sunday Star Times: "I thought he came on better and better and started to dominate the lineouts.
"I really felt he put his hand up to say 'hey, I'm in the locking area too, don't forget about me'."
Donnelly downplayed the praise, commenting: "I'm just taking it each week as it comes and just trying to play rugby.
"What happens, happens and I'll just take my chances when they come."
The All Blacks fly to the republic this week, while the second string take on Japan in Tokyo.