The Trotters were looking good to challenge the likes of Liverpool and Tottenham earlier in the season for a spot in the Europa League but fell away as injuries begun to take their toll.
Gretar Steinsson, Sam Ricketts, Stuart Holden, Mark Davies and Daniel Sturridge all missed last Saturday's defeat at Blackburn and Coyle is currently having to put square pegs in round holes in his patched up team.
Knight believes the club need to add quality players to Bolton in the summer if they want to continue to push for Europe next season.
"We haven't got the biggest squad but the players who have come in have tried hard," Knight told the Bolton News. "That's one thing we have got here, heart.
"But we do have to add to it as well. You can't just rely on heart, we need depth as well."