If we are not bringing in another defender as cover then we should certainly be looking beyond this season.
I think we have seen enough of Manny Duku now to appreciate that he is an effective and talented forward who, with the right service, can score not just at this level but probably at Premiership level as well. He also has skill as provider as well as finisher.
Looking at his CV, he seldom if ever spends more than a single season at any club.
At 28, he is coming into his prime, assuming his demands are reasonable, I would be looking to extend his contract for at least another two seasons and yo tie that up now before he starts coming to the attention of other clubs.