First-choice keeper Casteels, 21, has penned an extension that will see him stay at the Rhein-Neckar Arena until June 2017.
Meanwhile, understudy Grahl, 25, has committed his future to the German outfit until the summer of 2016.
Casteels, who has represented Belgium at five different age levels, has yet to keep a clean sheet in the Bundesliga this season, conceding 28 goals in 12 matches.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| C | Bayer LeverkusenB. Leverkusen | 34 | 28 | 6 | 0 | 89 | 24 | 65 | 90 |
| 2 | Stuttgart | 34 | 23 | 4 | 7 | 78 | 39 | 39 | 73 |
| 3 | Bayern MunichBayern | 34 | 23 | 3 | 8 | 94 | 45 | 49 | 72 |
| 4 | RB Leipzig | 34 | 19 | 8 | 7 | 77 | 39 | 38 | 65 |
| 5 | Borussia DortmundDortmund | 34 | 18 | 9 | 7 | 68 | 43 | 25 | 63 |
| 6 | Eintracht FrankfurtFrankfurt | 34 | 11 | 14 | 9 | 51 | 50 | 1 | 47 |
| 7 | Hoffenheim | 34 | 13 | 7 | 14 | 66 | 66 | 0 | 46 |
| 8 | Heidenheim | 34 | 10 | 12 | 12 | 50 | 55 | -5 | 42 |
| 9 | Werder Bremen | 34 | 11 | 9 | 14 | 48 | 54 | -6 | 42 |
| 10 | Freiburg | 34 | 11 | 9 | 14 | 45 | 58 | -13 | 42 |
| 11 | Augsburg | 34 | 10 | 9 | 15 | 50 | 60 | -10 | 39 |
| 12 | Wolfsburg | 34 | 10 | 7 | 17 | 41 | 56 | -15 | 37 |
| 13 | Mainz 05Mainz | 34 | 7 | 14 | 13 | 39 | 51 | -12 | 35 |
| 14 | Borussia MonchengladbachBorussia M'bach | 34 | 7 | 13 | 14 | 56 | 67 | -11 | 34 |
| 15 | Union BerlinUnion Berlin | 34 | 9 | 6 | 19 | 33 | 58 | -25 | 33 |
| 16 | VfL BochumVfL Bochum | 34 | 7 | 12 | 15 | 42 | 74 | -32 | 33 |
| R | FC Koln | 34 | 5 | 12 | 17 | 28 | 60 | -32 | 27 |
| R | SV Darmstadt 98Darmstadt | 34 | 3 | 8 | 23 | 30 | 86 | -56 | 17 |
| > Bundesliga Full Table | |||||||||
