Republic of Ireland striker Long had missed the club's last three matches with a dead leg prior to his introduction in the second half against Everton at Goodison Park on Wednesday evening.
The 26-year-old made an immediate impact, scoring with virtually his first touch, though it wasn't enough for the Baggies to avoid a 2-1 defeat.
Meanwhile, Argentine midfielder Yacob also came off the bench despite suffering a shoulder injury in Albion's last Premier League clash with Aston Villa.
Clarke was delighted to see two of his first choice stars back on the pitch but warned he was not going to take any risks with their fitness over the coming weeks.
"It was good for us that we got him [Long] back on the pitch last night," Clarke told the club's official website."He's been out for a number of weeks and hasn't trained very much with the team.
"Claudio also got a bit more time on the pitch. Second half, he grew into the game and looked more like his old self.
"It's great to get them out of the treatment room but it doesn't mean they're ready and firing to play matches.
"There is a process you have to go through, but I think in the next couple of games, we'll get the team back up to speed and hopefully back to the performances and results we got earlier in the season."
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