Midfielder Lee, 20, has put pen to paper on a one-year deal after making seven senior appearances for the O's.
Meanwhile, 18-year-old winger Semedo has penned a two-year contract after impressing in the youth team.
Orient start the new season at home to Barnet on August 8.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Birmingham CityBirmingham | 21 | 15 | 4 | 2 | 37 | 16 | 21 | 49 |
| 2 | Wrexham | 23 | 14 | 6 | 3 | 35 | 16 | 19 | 48 |
| 3 | Wycombe WanderersWycombe | 22 | 14 | 5 | 3 | 47 | 24 | 23 | 47 |
| 4 | Huddersfield TownHuddersfield | 22 | 13 | 4 | 5 | 36 | 19 | 17 | 43 |
| 5 | Stockport CountyStockport | 23 | 10 | 7 | 6 | 35 | 24 | 11 | 37 |
| 6 | Reading | 22 | 11 | 4 | 7 | 36 | 32 | 4 | 37 |
| 7 | Barnsley | 23 | 10 | 6 | 7 | 34 | 32 | 2 | 36 |
| 8 | Bolton WanderersBolton | 21 | 10 | 4 | 7 | 32 | 31 | 1 | 34 |
| 9 | Charlton AthleticCharlton | 22 | 9 | 6 | 7 | 27 | 21 | 6 | 33 |
| 10 | Leyton Orient | 22 | 9 | 4 | 9 | 28 | 20 | 8 | 31 |
| 11 | Mansfield TownMansfield | 21 | 9 | 4 | 8 | 27 | 24 | 3 | 31 |
| 12 | Lincoln CityLincoln | 23 | 8 | 7 | 8 | 28 | 29 | -1 | 31 |
| 13 | Exeter CityExeter | 22 | 9 | 4 | 9 | 26 | 27 | -1 | 31 |
| 14 | Stevenage | 21 | 8 | 5 | 8 | 18 | 20 | -2 | 29 |
| 15 | Blackpool | 22 | 7 | 7 | 8 | 30 | 33 | -3 | 28 |
| 16 | Wigan AthleticWigan | 22 | 7 | 6 | 9 | 21 | 20 | 1 | 27 |
| 17 | Rotherham UnitedRotherham | 21 | 6 | 6 | 9 | 20 | 23 | -3 | 24 |
| 18 | Peterborough UnitedPeterborough | 22 | 7 | 3 | 12 | 39 | 43 | -4 | 24 |
| 19 | Northampton TownNorthampton | 23 | 5 | 7 | 11 | 23 | 39 | -16 | 22 |
| 20 | Bristol Rovers | 22 | 6 | 4 | 12 | 19 | 35 | -16 | 22 |
| 21 | Crawley TownCrawley | 22 | 5 | 5 | 12 | 24 | 40 | -16 | 20 |
| 22 | Cambridge UnitedCambridge | 22 | 4 | 5 | 13 | 21 | 39 | -18 | 17 |
| 23 | Shrewsbury TownShrewsbury | 22 | 4 | 4 | 14 | 23 | 42 | -19 | 16 |
| 24 | Burton Albion | 22 | 2 | 7 | 13 | 18 | 35 | -17 | 13 |
| > League One Full Table | |||||||||
