The two players of Ghanaian descent have had opposite campaigns this season but could still win the treble under manager Xavi Alonso.
Fosu-Mensah has barely played this season and doesn’t seem to be in Alonso’s plans after failing to make a single Bundesliga appearance.
Frimpong, however, has been an integral part of the Leverkusen team, having featured in 45 matches in all competitions this season.
The wing-back has also contributed 14 goals and 12 assists as the Bundesliga side aims to finish the season with the treble.
Leverkusen have already wrapped up the league title and are also in the final of both the Europa League and the DFB Pokal after going unbeaten throughout the season.
Alonso’s side will, however, turn their attention to the Europa League final first, where they’ll be facing Alatanta at the Aviva Stadium in Ireland.
"I have enough things on my plate to think about than 'how good' or 'how nice' we are. In 10 days maybe I will stop and think we are doing something exceptional,” Alonso told TNT Sports
"We are not that stupid to say 'oh no, I don't care'. I'm really happy about it. Not to say it many more times, you become better because you are able to show it once again and that's why I try to push the guys. We don't take any game for granted and we don't rest on our laurels. That's my job."
Meanwhile, both Frimpong and Fosu-Mensah are still eligible to play for Ghana. Frimpong has been capped two times by the Netherlands while Fosu-Mensah has also played three times for the Dutch national team, making the duo eligible to switch nationality.