Since joining Albion on a season-long loan from Manchester City back in August, Sinclair has made just 10 appearances due to injuries, including six starts.
But, despite being fit since Mel's arrival, Sinclair has made just one 45-minute substitute outing under the Spaniard.
Sinclair's lack of activity resulted in talks between the two, with Mel suggesting given the club's perilous position, just one point above the drop zone, that he wanted more sweat than flair from his players.
"On Friday Scott spoke with me," Mel said. "I told him he is a good player, a good winger, but at the moment West Brom need hard work on the pitch.
"I assured him he will play in the future. Of course, it is normal he is disappointed he is not playing. All the players want to play, this is normal.
"But for me I can only pick 11 players, and this makes it difficult for me every day."
Mel is also hoping Argentina midfielder Claudio Yacob is fit for Albion's next clash with Manchester United at the Hawthorns on March 8.
Yacob missed Saturday's 1-1 home draw with Fulham with a hamstring injury sustained in the match with Chelsea 11 days previously.
Mel added: "He is a very important player for us in the middle. He is strong and is playing well.
"It is possible Yacob will be available to play against United."