The 49ers activated Celek (back) from the PUP list Monday, Matt Barrows of The Athletic reports.
Celek is eligible to play in Monday's game against the Seahawks, and his activation signals George Kittle (knee) -- who was considered doubtful -- will be inactive. He suited up in 15 games for the Niners last year, catching five passes for 90 yards and two scores. Celek will compete with Levine Toilolo and Ross Dwelley for reps, although the 31-year-old may be limited with minimal practice leading up to the contest.