After more than eight months on the sidelines, Subotic came on with 15 minutes remaining in Dortmund's 4-3 friendly win over 2.Bundesliga side Heidenheim on Saturday.
The Serbia international was delighted to be back and hopes to progressively get more game time as he looks to regain match fitness.
"My mind was everywhere," Subotic said.
"I wanted to help the team as good as possible but I have to get accustomed again to play against opponents hurling themselves into tackles.
"It's impossible to create this competitive environment in training. It's a great feeling to be back. It was great fun and I hope I get the opportunity to play a full half in the next game."
Subotic, 25, tore two ligaments in his knee in the Bundesliga in November and was ruled out for the rest of the season.
Dortmund coach Jurgen Klopp was thrilled to see the centre-back still unafraid to make tough challenges.
"He was grinning like a Cheshire cat, and was immediately in the thick of action. That's Neven," he said.
"He went into every tackle and was fully charged up."
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